PSY493H1 Lecture 2: Lecture 2 Neuroanatomy and Methods
Ida Henrietta Hyde
A pioneer in electrophysiology of single cell recordings
-
Invented the microelectrode
Thin glass tube inserted into cell membrane
○
Measures the voltage outside of the cell
○
Measures voltage differences
○
-
Phenology (pseudoscience): areas that are more used will be bigger - the study of cyclic
and seasonal natural phenomena, especially in relation to climate and plant and animal
life
Lateral ventricles: provide pressure, inflate the brain. Brain cavities filled with spinal fluid
(shock absorber)
Phylogenetic hierarchy
Brain stem contains many ancient structures responsible for vital functions
Brain stem = Hindbrain + Midbrain
○
-
-
Hindbrain: Medulla (survival, reflexes etc.)
Contains nuclei of cranial nerves (9-12) involved in facial motor and sensory signals
•
Most motor fibers are contralaterally organizedin the medulla
They cross from one side of the body to the other
○
•
Controls vital functions such as breathing and heart rate and reflexes •
Also contains set of neurons that make up the reticular activation system
Arousal, consciousness
○
•
Medulla lesion: die or go into coma •
Medulla is right under pons•
Hindbrain: Pons
Lies below the midbrain, above the medulla and in front of cerebellum •
Main connection b/w cortex & cerebellum •
Contains nuclei of cranial nerves (5-8)•
Many diverse functions including facial sensation, movements, saliva, tear
secretion and vestibular function (balance)
•
Includes the superior olive, a major relay hub for transmission of auditory input
from ear to brain
•
If lesion: facial paralyses, uncontrollable movement of tongue •
Hindbrain: Cerebellum
Blow midbrain
•
Main function: fine motor control and coordination
•
Important for coordinated flow of skilled movements (high level motor skills)
Riding a bike, painting, playing basketball, playing violin
○
•
Ipsilateral organization of motor control (different from medulla)
•
Controls higher cognitive processes
Timing, working memory, emotion
○
•
Tons of neurons!!
•
Midbrain
Includes the inferior and superior colliculi
Inferior colliculus
Sound localization
§
reflexive auditory orientation
§
○
Superior colliculus
Reflexive visual orientation, foveation
§
○
•
Location of dopamine nuclei:
Ventral tegmental area (VTA)
○
Substantia Nigra
Parkinson's: degradation in SN
§
Main cell nuclei for dopamine neuron are found here
§
○
•
Contains cranial nerve nuclei (3 & 4) •
Diencephalon: Thalamus & Hypothalamus
Thalamus
Sits on top of brain stem
○
Large bilateral mass of grey matter deep within the brain
○
Gateway (sensory relay) to the cortex, integrates all the signals coming from
the cranial nerves except olfactory nerve as it goes straight to amygdala
Medial geniculate (audition)
§
Lateral geniculate (vision)
§
○
Allows for reorganization and refinement of afferent input
○
-
Hypothalamus (Master gland)
Controls ANS & endocrine system
Hormones
§
○
Responsible for homeostatic functions
4 Fs
§
Light dark cycles, circadian rhythms (seasons)
Connection from retina to superchiasmatic nucleus
Light from electronics interrupt sleep by causing the pineal
gland to not secret melatonin
®
□
§
○
-
Basal Ganglia
Comprises many subcortical structures
Striatum: caudate, putamen & nucleus accumbens (most ventral part of
striatum, all drugs abuse, rich in dopamine, reward learning, motivation)
○
Globus pallidus
○
Substantia nigra
○
Subthalamic nucleus
○
-
Motor control: preparation and termination of action
-
Motivation, reward and addiction (pursing goals)
-
Limbic system (hippocampus and amygdala)
Hippocampus
Located in medial temporal lobes
Extends from fornix
§
○
Vital for memory consolidation (strengthening)
Transfer from STM -> LTM
§
○
Important for navigation
London cabbies have larger hippocampus
§
○
Damage -> anterograde amnesia
Patient H.M.: severe epilepsy, remove hippocampus, have anterograde
amnesia ( can’t form new memories)
§
○
Volume reduction in Alzheimer's Disease
Drugs treatment could reduce hippocampus volume
§
○
-
Amygdala
Located in medial temporal lobes, sits above hippocampus and has many
nuclei
○
Important for salience (anything that’s important to you)
Sensitive to intensity (we are very attuned to negative things; survival)
§
○
Emotion, memory processing and decision making
○
Fear and reward learning
○
Damage -> impairments in judgment and decision making
Not afraid of anything
§
Tumour on amygdala might causes impulsive behaviour with
combination of other factors
§
○
-
Cerebral cortex
Cortex = Bark
-
Most recent evolutionary expansion
-
~1.5-5.5 mm thick
-
6 layers of cells
-
Convoluted and wrinkled -> maximize surface area
Gyri/gyrus: bump, protruding rounded surfaces (folds)
○
Sulci/sulcus: valley b/w gyri
○
Fissure: very deep sulcus
○
-
Separated into 2 halves but can communicates
Corpus callosum ( white matter tract)
○
Anterior commissure
Connected temporal lobes
§
○
○
-
The important lobes and sulci
Frontal lobe
-
Temporal lobe
-
Parietal lobe
-
Occipital lobe
-
Insula
Buried deep within the lateral sulcus (in b/w temporal, frontal and parietal lobe)
-
Primary gustatory cortex (taste)
-
Also area important for disgust
Physical and moral
○
-
Central sulcus also separate the primary motor cortex (premotor) and primary
somatosensory cortex (post motor)
Primary Motor Cortex (M1)
Organization around specific attribute of physical world
Specific body area controlled by specific motor region
○
-
Distortion relative to physical world
Parts of body with fine motor control are larger (face, digits)
○
-
Mapping is upside-down
Body parts are represented inversely in cortex
○
-
Hemiplegia (often from stroke) results in paralysis on contralateral side of body
Occurs with unilateral damage to M1 and combined with damage to basal
ganglia
○
-
Primary Somatosensory Cortex (S1) -postcentral gyrus
Organization around specific attribute of physical world
Mapped based on area of body that receives tactile input (touch,
temperature, pain, etc.)
○
-
Distortion relative to physical world
Representation of body parts proportional to density of touch receptors
○
-
Mapping is represented upside-down in cortex
-
Neurotransmitters
Amino acids
Glutamate (CNS) - excitatory a.
GABA (CNS) - inhibitory b.
Aspartate (PNS)c.
Glycine (PNS)d.
1.
"System" neurotransmitters
Acetylcholine a.
Dopamineb.
Norepinephrine (noradrenaline)c.
Serotonin d.
2.
Effects of many neurotransmitters depends upon the receptor subtype they bind to
Amino acids (CNS)
Glutamate Gamma-aminobutyric acid (GABA)
Excitatory
-
Plays role in epilepsy
-
Excess causes
cytotoxicity
-
Precursor to GABA
-
Inhibitory
-
Two kinds of receptors
GABA A (ionotropic) - ion channel•
GABA B (metabotropic) - G couple receptor protein•
-
Activation results in sedation and sleep
Alcohol activates GABA•
Brain becomes overactive, can’t downgrade the
activity, could die
•
-
Anxiolytics and Benzodiazepines (i.e. Xanax) activate GABA
-
Neurotransmitters systems
Acetylcholine
-
Monoamines:
Dopamine
○
Norepinephrine (noradrenaline)
○
Serotonin (from tryptophan)
○
-
Cholinergic system: Acetylcholine (Ach)
2 main receptor subtypes:
Nicotinic (ionotropic)
○
Muscarinic (metabotropic)
○
-
Nuclei in pons, midbrain and basal forebrain
-
Maintains cortical excitability, decreases with anaesthesia
-
Selective attention ( filter out distractive info)
-
Motivation & reward
-
Dopaminergic system: Dopamine (DA)
3 subsytems:
Nigrostriatal (substantia nigra)
Movement - Parkinson's
§
○
Mesolimbic (VTA) - main dopamine producer
Prediction error, reward, motivation
§
○
Mesocortical (VTA)
Working memory
§
○
-
2 main receptor subtype families
D1 (excitatory)
○
D2 (inhibitory)
○
-
Noradrenergic system: Norepinephrine (NE)
Nuclei in Locus Coeruleus
-
Mobilizing the brain by enhancing sensory processing
-
Role in arousal and attention
Shuts off during REM sleep
○
-
Also main NT for sympathetic nervous system
Fight or flight response
○
-
Vessel constrictor: AP pen, shot in epinephrine, increase BP
-
Serotonergic system: Serotonin (5-HT)
Main source in Raphe Nuclei in brain stem
-
Controls transmission of dopamine and epinephrine
-
Many effects
Arousal, mood, anxiety
○
Eating
○
Pain
○
Sexual behaviours
○
Memory
○
-
Putative (uncertain) role in depression
Selective serotonin reuptake inhibitors (SSRIs)
Works immediately, but the actual effects takes weeks
§
○
-
Methods in Cognitive Neuroscience
Lesion method 1.
Brain imaging
Electrical/magnetic
EEGi.
MEG ii.
Single cell iii.
a.
Metabolic
fMRIi.
PETii.
EROS iii.
b.
2.
Brain lesion method: Neuropsychology
IF: function X is disrupted by lesion to brain region Y
-
THEN: brain region Y supports function X
-
Suggests a causal link b/w region and cognitive function
-
Patient Gage
-
Two conceptual approaches
What function is supported by a given
brain region?
What brain region supports a given cognitive
function?
Examine a group of patients with similar
lesions
-
Compare to a control group of patients
with different lesions
-
Examine a group of patients with similar
cognitive impairment
-
Then examine the brain regions common
with deficit
-
Human and non-human lesion studies
Human neuropsychology Non-human neuropsychology
Acquired brain damage
Naturally occurring neurological
condition or surgical treatment of
condition
-
Not under control of experimenter
Location and extend of lesion,
demographics
-
Single-case or group studies
Under control of experimenter
Lesion location and size, sample,
environment, age
-
Precise brain structures selected for
lesioning
Using surgical and neurotoxic
procedures (permanent or reversible
lesions)
-
Double Dissociation
Determine whether two functions are independent
Patient with damage to area X has impaired function A, but function B is fine
○
Patient with damage to area Y has impaired function B, but function A is fine
○
-
Example:
lesion to Broca's area (X) impairs speech production (A) but not
comprehension (B)
○
Lesion to Wernicke's area (Y) impairs comprehension (B) but not production
(A)
○
-
Brain Lesion Study Limitations
Disconnection syndrome: area X may not participate directly in function A but may
disconnect two critical brain regions that are critical for function A
E.g. split-brain patients
Serving the fibers of the corpus callosum leads to certain cognitive
impairments
§
But it’s not the corpus callosum that carries out these functions!
§
○
-
Lateralization of language
For the majority of people language centers are located in left hemisphere
-
In split brain patients the left and right hemispheres cannot communicate
-
The visual system is contralaterally organized
So images presented in left visual field are represented neural in right
hemisphere
For split brain, present stuff at left VF -> right hemisphere -> cannot
verbally say the item but can point towards the item.
§
○
-
Sitting on a 2 legged stool
Function may be unrelated to area X but actually related to the brain with area X
intact
-
Ascribe non-functionality to broken leg: infer that specific leg is necessary for
functioning of stool
Wrong! All legs participate
○
Stool failure is result of system level dysfunction
○
-
Brain involves 100 billion interconnected neurons
Relies on both localization of function and distributed processing!
○
Also compensatory reorganization occurs!
○
-
Brain imaging
Anatomical/structure imaging
CT, MRI
○
-
Functional/dynamic: physiological imaging
Access how neural activity varies over time
Electrical
Intracranial and/or scalp EEG, ERP □
§
Metabolic
PET, fMRI □
§
○
-
Functional brain imaging: EEG(electroencephalogram)
Measures voltage fluctuations from electrical signals of neuron populations
-
Electrodes measure underlying electrical activity through the scalp
-
Difference b/w designated reference (i.e. earlobe, mastoid) and recording
electrodes produces and electrical potential
-
Sums activity from all over the brain
Great temporal solution
○
-
Depicts time course of global brain activation
-
Event-related potentials (ERPs) are a special case of EEG: brief changes in signal
Average EEG signal from many trials
○
Lock the signal to the onset of stimulus or a motor response and you get ERP
Large background oscillations of the EEG signal make ERP detection
from single trial impossible
§
Need to average hundreds of trials -> remove EEG background, reveal
ERP
§
○
Many different kinds of ERPs with different signatures and associated with
different cognitive functions
○
-
Pros Cons
Good temporal resolution
-
ERPs can tell us about cognitive processes
-
Much more affordable than MRI/fMRI
-
Poor spatial resolution
-
Cannot access deep brain structures (e.g.
medial temporal lobe)
-
Functional brain imaging: MEG
Records magnetic fields generated by electrical currents using SQUID arrays
(superconducting quantum interference devices)
-
Great temporal and spatial resolution
-
Magnetic fields are less distorted by skull, scalp and movement interference
-
MEG is sensitive to neocortical activity
Epilepsy and neurosurgery localization
○
Often paired with fMRI
○
-
Structural brain imaging: CT scans (computerized axial tomography)
First modern technique before MRI
-
Allows for localization of brain damage
-
Utilizes X-rays for visualization
-
Different tissues have different desnsities
X-rays (sub-par spatial resolution) pass easily through low-densities (water,
ventriculus fluid, blood) but are absorbed by high-densities like bone
Density gradient
the darker it is the less dense it is□
Black -> White
CSF < brain tissue < blood < bone
®
□
§
○
-
Structure brain imaging: MRI (Magnetic Resonance Imaging)
Quest for better resolution and more brain coverage requires a very strong magnet!
1 Tesla (T) = 10,000 Gauss
○
Earth's magnetic field = 0.5 Gauss
○
4T magnet is 80,000 times the strength of the Earth's magnetic field
○
A lot of helium
○
-
Uses a large magnet measure in Tesla (field strength)
-
Combined with radio frequency pulse of a specific resonance
-
This creates an image
Many organic elements in the body are magnetic
Hydrogen: most abundant in the body
§
Protons spin around a random axis
§
○
When placed inside a magnetic field the protons all become aligned in parallel
○
A radio frequency (RF) pulse sequence is used to push protons put of
alignment with the magnetic field
○
The time it takes for the protons to revert back to original orientation is
measured through the head coil
○
Protons relax at different rates in different tissues which produces a
gradient that reconstructed as a image
○
-
Advantages of MRI over CT
No x-rays
○
Superior spatial resolution
○
-
MRI vs. fMRI
High resolution (1mm)
§
One image
§
2D slices of the brain
§
○
-
fMRI
Neurons get O2 via hemoglobin in RBC
-
When neuronal activity increases O2 demand increases, so more blood flow
-
Oxygenated blood is diamagnetic (magnetically repelled) and paramagnetic when
deoxygenated (magnetically attracted)
These differences in oxygenation and their magnetic properties create
differences in MR signal, which can be used to infer brain activity
○
-
This is known as blood oxygenation level dependent (BOLD) imaging
-
Hemodynamic response
Hemodynamic response (HR) is change in regional cerebral blood flow (rCBF)
over time
○
Neural response to stimulus happens in ms
○
HR peaks 5-10 sec post stimulus (SLOW)
Starts about 2s after stimulus presentation
§
○
Experimental design
Block designs
Examine extended HR across same trial type
§
○
Event-related designs
HR for different, individual trials
§
Allows examination of trial specific HR, such as predicting memory later
on from HR
§
○
Subtractive logic
fMRI detects a change in signal form one condition to another - therefore you
must always contrast 2 conditions
○
Functional images are subtracted from one another
○
Superimposed on anatomical image
○
Importance of well-designed baseline!
Depend on your questions: e.g. all regions specific to viewing a face or
all regions involved in viewing a face
§
○
PROS CONS
Non-invasive, no radiation
-
Can do multiple scans with same person
-
Great spatial and good temporal resolution
-
People love images
-
Very expensive
-
Correlational
-
People love images
-
Positron Emission Tomography (PET)
Measures local changes in cerebral blood flow (rCBF)
-
Measures rCBF over a few minute period (doesn't have the best temporal)
-
Radioactive isotopes tracers introduced into the body
Isotopes rapidly decay -> this decay is measured to produce the signal
○
-
PROS CONS
Track multiple metabolic processes
Specific NT can be labeled and
measured (isotopes tag to specific NT
receptor sites)
•
-Invasive: radioactive isotopes
Can only be administered limited
number of times
•
-
Highly limited temporal resolution
Limited by the half life of the
isotope used
Oxygen-15 gives an image of
brain activity averaged over
1.5 mins; fMRI average over
2s
○
•
-
Diffusion Tensor Imaging (DTI)
3D modelling technique that shows neuroanatomical connectivity by measuring
tissue bundles
-
Tractography maps show white matter connectivity via water flow measurements
in tissue
-
Looking at neurodegeneration
-
Transcranial Magnetic Stimulation (TMS)
Localized magnetic pulses alter electrical activity of neurons
-
TMS coils can activate or deactivate a region of neurons
-
Determining causation
○Brain region A appears to be active in decision-making task (fMRI evidence)
○Administer TMS to region A and to different brain region B (control area) not
involved in decision making task. See how performance differs
○If TMS on region A influences task, but TMS on region B does not, shows
evidence suggesting region A is causally linked to the mental process engaged
by task.
-
Optic imaging
-Laser of infrared light
-Sensors detect distortions in light
-Great temporal and spatial resolution
-Drawback is only cortical activity can be detected
Reflexive: involuntary
Foveation: voluntary or involuntary
Central (Rolandic) sulcus: separate frontal and parietal
Sylvian (lateral) sulcus: separate temporal from frontal
and parietal
Agonist: a chemical binds to
receptor and mimics effects of
the neurotransmitter
Antagonist: a chemical that binds
to receptor and inhibits or block
effect of the neurotransmitter
Catecholamines (from tyrosine)
Low resolution
-
Many images / 2 s
-
Lecture 2
Thursday, May 24, 2018
3:51 PM
Ida Henrietta Hyde
A pioneer in electrophysiology of single cell recordings
-
Invented the microelectrode
Thin glass tube inserted into cell membrane
○
Measures the voltage outside of the cell
○
Measures voltage differences
○
-
Phenology (pseudoscience): areas that are more used will be bigger - the study of cyclic
and seasonal natural phenomena, especially in relation to climate and plant and animal
life
Lateral ventricles: provide pressure, inflate the brain. Brain cavities filled with spinal fluid
(shock absorber)
Phylogenetic hierarchy
Brain stem contains many ancient structures responsible for vital functions
Brain stem = Hindbrain + Midbrain
○
-
-
Hindbrain: Medulla (survival, reflexes etc.)
Contains nuclei of cranial nerves (9-12) involved in facial motor and sensory signals
•
Most motor fibers are contralaterally organizedin the medulla
They cross from one side of the body to the other
○
•
Controls vital functions such as breathing and heart rate and reflexes
•
Also contains set of neurons that make up the reticular activation system
Arousal, consciousness
○
•
Medulla lesion: die or go into coma
•
Medulla is right under pons
•
Hindbrain: Pons
Lies below the midbrain, above the medulla and in front of cerebellum
•
Main connection b/w cortex & cerebellum
•
Contains nuclei of cranial nerves (5-8)
•
Many diverse functions including facial sensation, movements, saliva, tear
secretion and vestibular function (balance)
•
Includes the superior olive, a major relay hub for transmission of auditory input
from ear to brain
•
If lesion: facial paralyses, uncontrollable movement of tongue
•
Hindbrain: Cerebellum
Blow midbrain
•
Main function: fine motor control and coordination
•
Important for coordinated flow of skilled movements (high level motor skills)
Riding a bike, painting, playing basketball, playing violin
○
•
Ipsilateral organization of motor control (different from medulla)
•
Controls higher cognitive processes
Timing, working memory, emotion
○
•
Tons of neurons!!
•
Midbrain
Includes the inferior and superior colliculi
Inferior colliculus
Sound localization
§
reflexive auditory orientation
§
○
Superior colliculus
Reflexive visual orientation, foveation
§
○
•
Location of dopamine nuclei:
Ventral tegmental area (VTA)
○
Substantia Nigra
Parkinson's: degradation in SN
§
Main cell nuclei for dopamine neuron are found here
§
○
•
Contains cranial nerve nuclei (3 & 4) •
Diencephalon: Thalamus & Hypothalamus
Thalamus
Sits on top of brain stem
○
Large bilateral mass of grey matter deep within the brain
○
Gateway (sensory relay) to the cortex, integrates all the signals coming from
the cranial nerves except olfactory nerve as it goes straight to amygdala
Medial geniculate (audition)
§
Lateral geniculate (vision)
§
○
Allows for reorganization and refinement of afferent input
○
-
Hypothalamus (Master gland)
Controls ANS & endocrine system
Hormones
§
○
Responsible for homeostatic functions
4 Fs
§
Light dark cycles, circadian rhythms (seasons)
Connection from retina to superchiasmatic nucleus
Light from electronics interrupt sleep by causing the pineal
gland to not secret melatonin
®
□
§
○
-
Basal Ganglia
Comprises many subcortical structures
Striatum: caudate, putamen & nucleus accumbens (most ventral part of
striatum, all drugs abuse, rich in dopamine, reward learning, motivation)
○
Globus pallidus
○
Substantia nigra
○
Subthalamic nucleus
○
-
Motor control: preparation and termination of action
-
Motivation, reward and addiction (pursing goals)
-
Limbic system (hippocampus and amygdala)
Hippocampus
Located in medial temporal lobes
Extends from fornix
§
○
Vital for memory consolidation (strengthening)
Transfer from STM -> LTM
§
○
Important for navigation
London cabbies have larger hippocampus
§
○
Damage -> anterograde amnesia
Patient H.M.: severe epilepsy, remove hippocampus, have anterograde
amnesia ( can’t form new memories)
§
○
Volume reduction in Alzheimer's Disease
Drugs treatment could reduce hippocampus volume
§
○
-
Amygdala
Located in medial temporal lobes, sits above hippocampus and has many
nuclei
○
Important for salience (anything that’s important to you)
Sensitive to intensity (we are very attuned to negative things; survival)
§
○
Emotion, memory processing and decision making
○
Fear and reward learning
○
Damage -> impairments in judgment and decision making
Not afraid of anything
§
Tumour on amygdala might causes impulsive behaviour with
combination of other factors
§
○
-
Cerebral cortex
Cortex = Bark
-
Most recent evolutionary expansion
-
~1.5-5.5 mm thick
-
6 layers of cells
-
Convoluted and wrinkled -> maximize surface area
Gyri/gyrus: bump, protruding rounded surfaces (folds)
○
Sulci/sulcus: valley b/w gyri
○
Fissure: very deep sulcus
○
-
Separated into 2 halves but can communicates
Corpus callosum ( white matter tract)
○
Anterior commissure
Connected temporal lobes
§
○
○
-
The important lobes and sulci
Frontal lobe
-
Temporal lobe
-
Parietal lobe
-
Occipital lobe
-
Insula
Buried deep within the lateral sulcus (in b/w temporal, frontal and parietal lobe)
-
Primary gustatory cortex (taste)
-
Also area important for disgust
Physical and moral
○
-
Central sulcus also separate the primary motor cortex (premotor) and primary
somatosensory cortex (post motor)
Primary Motor Cortex (M1)
Organization around specific attribute of physical world
Specific body area controlled by specific motor region
○
-
Distortion relative to physical world
Parts of body with fine motor control are larger (face, digits)
○
-
Mapping is upside-down
Body parts are represented inversely in cortex
○
-
Hemiplegia (often from stroke) results in paralysis on contralateral side of body
Occurs with unilateral damage to M1 and combined with damage to basal
ganglia
○
-
Primary Somatosensory Cortex (S1) -postcentral gyrus
Organization around specific attribute of physical world
Mapped based on area of body that receives tactile input (touch,
temperature, pain, etc.)
○
-
Distortion relative to physical world
Representation of body parts proportional to density of touch receptors
○
-
Mapping is represented upside-down in cortex
-
Neurotransmitters
Amino acids
Glutamate (CNS) - excitatory a.
GABA (CNS) - inhibitory b.
Aspartate (PNS)c.
Glycine (PNS)d.
1.
"System" neurotransmitters
Acetylcholine a.
Dopamineb.
Norepinephrine (noradrenaline)c.
Serotonin d.
2.
Effects of many neurotransmitters depends upon the receptor subtype they bind to
Amino acids (CNS)
Glutamate Gamma-aminobutyric acid (GABA)
Excitatory
-
Plays role in epilepsy
-
Excess causes
cytotoxicity
-
Precursor to GABA
-
Inhibitory
-
Two kinds of receptors
GABA A (ionotropic) - ion channel•
GABA B (metabotropic) - G couple receptor protein•
-
Activation results in sedation and sleep
Alcohol activates GABA•
Brain becomes overactive, can’t downgrade the
activity, could die
•
-
Anxiolytics and Benzodiazepines (i.e. Xanax) activate GABA
-
Neurotransmitters systems
Acetylcholine
-
Monoamines:
Dopamine
○
Norepinephrine (noradrenaline)
○
Serotonin (from tryptophan)
○
-
Cholinergic system: Acetylcholine (Ach)
2 main receptor subtypes:
Nicotinic (ionotropic)
○
Muscarinic (metabotropic)
○
-
Nuclei in pons, midbrain and basal forebrain
-
Maintains cortical excitability, decreases with anaesthesia
-
Selective attention ( filter out distractive info)
-
Motivation & reward
-
Dopaminergic system: Dopamine (DA)
3 subsytems:
Nigrostriatal (substantia nigra)
Movement - Parkinson's
§
○
Mesolimbic (VTA) - main dopamine producer
Prediction error, reward, motivation
§
○
Mesocortical (VTA)
Working memory
§
○
-
2 main receptor subtype families
D1 (excitatory)
○
D2 (inhibitory)
○
-
Noradrenergic system: Norepinephrine (NE)
Nuclei in Locus Coeruleus
-
Mobilizing the brain by enhancing sensory processing
-
Role in arousal and attention
Shuts off during REM sleep
○
-
Also main NT for sympathetic nervous system
Fight or flight response
○
-
Vessel constrictor: AP pen, shot in epinephrine, increase BP
-
Serotonergic system: Serotonin (5-HT)
Main source in Raphe Nuclei in brain stem
-
Controls transmission of dopamine and epinephrine
-
Many effects
Arousal, mood, anxiety
○
Eating
○
Pain
○
Sexual behaviours
○
Memory
○
-
Putative (uncertain) role in depression
Selective serotonin reuptake inhibitors (SSRIs)
Works immediately, but the actual effects takes weeks
§
○
-
Methods in Cognitive Neuroscience
Lesion method 1.
Brain imaging
Electrical/magnetic
EEGi.
MEG ii.
Single cell iii.
a.
Metabolic
fMRIi.
PETii.
EROS iii.
b.
2.
Brain lesion method: Neuropsychology
IF: function X is disrupted by lesion to brain region Y
-
THEN: brain region Y supports function X
-
Suggests a causal link b/w region and cognitive function
-
Patient Gage
-
Two conceptual approaches
What function is supported by a given
brain region?
What brain region supports a given cognitive
function?
Examine a group of patients with similar
lesions
-
Compare to a control group of patients
with different lesions
-
Examine a group of patients with similar
cognitive impairment
-
Then examine the brain regions common
with deficit
-
Human and non-human lesion studies
Human neuropsychology Non-human neuropsychology
Acquired brain damage
Naturally occurring neurological
condition or surgical treatment of
condition
-
Not under control of experimenter
Location and extend of lesion,
demographics
-
Single-case or group studies
Under control of experimenter
Lesion location and size, sample,
environment, age
-
Precise brain structures selected for
lesioning
Using surgical and neurotoxic
procedures (permanent or reversible
lesions)
-
Double Dissociation
Determine whether two functions are independent
Patient with damage to area X has impaired function A, but function B is fine
○
Patient with damage to area Y has impaired function B, but function A is fine
○
-
Example:
lesion to Broca's area (X) impairs speech production (A) but not
comprehension (B)
○
Lesion to Wernicke's area (Y) impairs comprehension (B) but not production
(A)
○
-
Brain Lesion Study Limitations
Disconnection syndrome: area X may not participate directly in function A but may
disconnect two critical brain regions that are critical for function A
E.g. split-brain patients
Serving the fibers of the corpus callosum leads to certain cognitive
impairments
§
But it’s not the corpus callosum that carries out these functions!
§
○
-
Lateralization of language
For the majority of people language centers are located in left hemisphere
-
In split brain patients the left and right hemispheres cannot communicate
-
The visual system is contralaterally organized
So images presented in left visual field are represented neural in right
hemisphere
For split brain, present stuff at left VF -> right hemisphere -> cannot
verbally say the item but can point towards the item.
§
○
-
Sitting on a 2 legged stool
Function may be unrelated to area X but actually related to the brain with area X
intact
-
Ascribe non-functionality to broken leg: infer that specific leg is necessary for
functioning of stool
Wrong! All legs participate
○
Stool failure is result of system level dysfunction
○
-
Brain involves 100 billion interconnected neurons
Relies on both localization of function and distributed processing!
○
Also compensatory reorganization occurs!
○
-
Brain imaging
Anatomical/structure imaging
CT, MRI
○
-
Functional/dynamic: physiological imaging
Access how neural activity varies over time
Electrical
Intracranial and/or scalp EEG, ERP □
§
Metabolic
PET, fMRI □
§
○
-
Functional brain imaging: EEG(electroencephalogram)
Measures voltage fluctuations from electrical signals of neuron populations
-
Electrodes measure underlying electrical activity through the scalp
-
Difference b/w designated reference (i.e. earlobe, mastoid) and recording
electrodes produces and electrical potential
-
Sums activity from all over the brain
Great temporal solution
○
-
Depicts time course of global brain activation
-
Event-related potentials (ERPs) are a special case of EEG: brief changes in signal
Average EEG signal from many trials
○
Lock the signal to the onset of stimulus or a motor response and you get ERP
Large background oscillations of the EEG signal make ERP detection
from single trial impossible
§
Need to average hundreds of trials -> remove EEG background, reveal
ERP
§
○
Many different kinds of ERPs with different signatures and associated with
different cognitive functions
○
-
Pros Cons
Good temporal resolution
-
ERPs can tell us about cognitive processes
-
Much more affordable than MRI/fMRI
-
Poor spatial resolution
-
Cannot access deep brain structures (e.g.
medial temporal lobe)
-
Functional brain imaging: MEG
Records magnetic fields generated by electrical currents using SQUID arrays
(superconducting quantum interference devices)
-
Great temporal and spatial resolution
-
Magnetic fields are less distorted by skull, scalp and movement interference
-
MEG is sensitive to neocortical activity
Epilepsy and neurosurgery localization
○
Often paired with fMRI
○
-
Structural brain imaging: CT scans (computerized axial tomography)
First modern technique before MRI
-
Allows for localization of brain damage
-
Utilizes X-rays for visualization
-
Different tissues have different desnsities
X-rays (sub-par spatial resolution) pass easily through low-densities (water,
ventriculus fluid, blood) but are absorbed by high-densities like bone
Density gradient
the darker it is the less dense it is□
Black -> White
CSF < brain tissue < blood < bone
®
□
§
○
-
Structure brain imaging: MRI (Magnetic Resonance Imaging)
Quest for better resolution and more brain coverage requires a very strong magnet!
1 Tesla (T) = 10,000 Gauss
○
Earth's magnetic field = 0.5 Gauss
○
4T magnet is 80,000 times the strength of the Earth's magnetic field
○
A lot of helium
○
-
Uses a large magnet measure in Tesla (field strength)
-
Combined with radio frequency pulse of a specific resonance
-
This creates an image
Many organic elements in the body are magnetic
Hydrogen: most abundant in the body
§
Protons spin around a random axis
§
○
When placed inside a magnetic field the protons all become aligned in parallel
○
A radio frequency (RF) pulse sequence is used to push protons put of
alignment with the magnetic field
○
The time it takes for the protons to revert back to original orientation is
measured through the head coil
○
Protons relax at different rates in different tissues which produces a
gradient that reconstructed as a image
○
-
Advantages of MRI over CT
No x-rays
○
Superior spatial resolution
○
-
MRI vs. fMRI
High resolution (1mm)
§
One image
§
2D slices of the brain
§
○
-
fMRI
Neurons get O2 via hemoglobin in RBC
-
When neuronal activity increases O2 demand increases, so more blood flow
-
Oxygenated blood is diamagnetic (magnetically repelled) and paramagnetic when
deoxygenated (magnetically attracted)
These differences in oxygenation and their magnetic properties create
differences in MR signal, which can be used to infer brain activity
○
-
This is known as blood oxygenation level dependent (BOLD) imaging
-
Hemodynamic response
Hemodynamic response (HR) is change in regional cerebral blood flow (rCBF)
over time
○
Neural response to stimulus happens in ms
○
HR peaks 5-10 sec post stimulus (SLOW)
Starts about 2s after stimulus presentation
§
○
Experimental design
Block designs
Examine extended HR across same trial type
§
○
Event-related designs
HR for different, individual trials
§
Allows examination of trial specific HR, such as predicting memory later
on from HR
§
○
Subtractive logic
fMRI detects a change in signal form one condition to another - therefore you
must always contrast 2 conditions
○
Functional images are subtracted from one another
○
Superimposed on anatomical image
○
Importance of well-designed baseline!
Depend on your questions: e.g. all regions specific to viewing a face or
all regions involved in viewing a face
§
○
PROS CONS
Non-invasive, no radiation
-
Can do multiple scans with same person
-
Great spatial and good temporal resolution
-
People love images
-
Very expensive
-
Correlational
-
People love images
-
Positron Emission Tomography (PET)
Measures local changes in cerebral blood flow (rCBF)
-
Measures rCBF over a few minute period (doesn't have the best temporal)
-
Radioactive isotopes tracers introduced into the body
Isotopes rapidly decay -> this decay is measured to produce the signal
○
-
PROS CONS
Track multiple metabolic processes
Specific NT can be labeled and
measured (isotopes tag to specific NT
receptor sites)
•
-Invasive: radioactive isotopes
Can only be administered limited
number of times
•
-
Highly limited temporal resolution
Limited by the half life of the
isotope used
Oxygen-15 gives an image of
brain activity averaged over
1.5 mins; fMRI average over
2s
○
•
-
Diffusion Tensor Imaging (DTI)
3D modelling technique that shows neuroanatomical connectivity by measuring
tissue bundles
-
Tractography maps show white matter connectivity via water flow measurements
in tissue
-
Looking at neurodegeneration
-
Transcranial Magnetic Stimulation (TMS)
Localized magnetic pulses alter electrical activity of neurons
-
TMS coils can activate or deactivate a region of neurons
-
Determining causation
○Brain region A appears to be active in decision-making task (fMRI evidence)
○Administer TMS to region A and to different brain region B (control area) not
involved in decision making task. See how performance differs
○If TMS on region A influences task, but TMS on region B does not, shows
evidence suggesting region A is causally linked to the mental process engaged
by task.
-
Optic imaging
-Laser of infrared light
-Sensors detect distortions in light
-Great temporal and spatial resolution
-Drawback is only cortical activity can be detected
Reflexive: involuntary
Foveation: voluntary or involuntary
Central (Rolandic) sulcus: separate frontal and parietal
Sylvian (lateral) sulcus: separate temporal from frontal
and parietal
Agonist: a chemical binds to
receptor and mimics effects of
the neurotransmitter
Antagonist: a chemical that binds
to receptor and inhibits or block
effect of the neurotransmitter
Catecholamines (from tyrosine)
Low resolution
-
Many images / 2 s
-
Lecture 2
Thursday, May 24, 2018 3:51 PM
Ida Henrietta Hyde
A pioneer in electrophysiology of single cell recordings
-
Invented the microelectrode
Thin glass tube inserted into cell membrane
○
Measures the voltage outside of the cell
○
Measures voltage differences
○
-
Phenology (pseudoscience): areas that are more used will be bigger - the study of cyclic
and seasonal natural phenomena, especially in relation to climate and plant and animal
life
Lateral ventricles: provide pressure, inflate the brain. Brain cavities filled with spinal fluid
(shock absorber)
Phylogenetic hierarchy
Brain stem contains many ancient structures responsible for vital functions
Brain stem = Hindbrain + Midbrain
○
-
-
Hindbrain: Medulla (survival, reflexes etc.)
Contains nuclei of cranial nerves (9-12) involved in facial motor and sensory signals•
Most motor fibers are contralaterally organizedin the medulla
They cross from one side of the body to the other
○
•
Controls vital functions such as breathing and heart rate and reflexes •
Also contains set of neurons that make up the reticular activation system
Arousal, consciousness
○
•
Medulla lesion: die or go into coma •
Medulla is right under pons•
Hindbrain: Pons
Lies below the midbrain, above the medulla and in front of cerebellum •
Main connection b/w cortex & cerebellum •
Contains nuclei of cranial nerves (5-8)•
Many diverse functions including facial sensation, movements, saliva, tear
secretion and vestibular function (balance)
•
Includes the superior olive, a major relay hub for transmission of auditory input
from ear to brain
•
If lesion: facial paralyses, uncontrollable movement of tongue •
Hindbrain: Cerebellum
Blow midbrain
•
Main function: fine motor control and coordination
•
Important for coordinated flow of skilled movements (high level motor skills)
Riding a bike, painting, playing basketball, playing violin
○
•
Ipsilateral organization of motor control (different from medulla)
•
Controls higher cognitive processes
Timing, working memory, emotion
○
•
Tons of neurons!!
•
Midbrain
Includes the inferior and superior colliculi
Inferior colliculus
Sound localization
§
reflexive auditory orientation
§
○
Superior colliculus
Reflexive visual orientation, foveation
§
○
•
Location of dopamine nuclei:
Ventral tegmental area (VTA)
○
Substantia Nigra
Parkinson's: degradation in SN
§
Main cell nuclei for dopamine neuron are found here
§
○
•
Contains cranial nerve nuclei (3 & 4)
•
Diencephalon: Thalamus & Hypothalamus
Thalamus
Sits on top of brain stem
○
Large bilateral mass of grey matter deep within the brain
○
Gateway (sensory relay) to the cortex, integrates all the signals coming from
the cranial nerves except olfactory nerve as it goes straight to amygdala
Medial geniculate (audition)
§
Lateral geniculate (vision)
§
○
Allows for reorganization and refinement of afferent input
○
-
Hypothalamus (Master gland)
Controls ANS & endocrine system
Hormones
§
○
Responsible for homeostatic functions
4 Fs
§
Light dark cycles, circadian rhythms (seasons)
Connection from retina to superchiasmatic nucleus
Light from electronics interrupt sleep by causing the pineal
gland to not secret melatonin
®
□
§
○
-
Basal Ganglia
Comprises many subcortical structures
Striatum: caudate, putamen & nucleus accumbens (most ventral part of
striatum, all drugs abuse, rich in dopamine, reward learning, motivation)
○
Globus pallidus
○
Substantia nigra
○
Subthalamic nucleus
○
-
Motor control: preparation and termination of action
-
Motivation, reward and addiction (pursing goals)
-
Limbic system (hippocampus and amygdala)
Hippocampus
Located in medial temporal lobes
Extends from fornix
§
○
Vital for memory consolidation (strengthening)
Transfer from STM -> LTM
§
○
Important for navigation
London cabbies have larger hippocampus
§
○
Damage -> anterograde amnesia
Patient H.M.: severe epilepsy, remove hippocampus, have anterograde
amnesia ( can’t form new memories)
§
○
Volume reduction in Alzheimer's Disease
Drugs treatment could reduce hippocampus volume
§
○
-
Amygdala
Located in medial temporal lobes, sits above hippocampus and has many
nuclei
○
Important for salience (anything that’s important to you)
Sensitive to intensity (we are very attuned to negative things; survival)
§
○
Emotion, memory processing and decision making
○
Fear and reward learning
○
Damage -> impairments in judgment and decision making
Not afraid of anything
§
Tumour on amygdala might causes impulsive behaviour with
combination of other factors
§
○
-
Cerebral cortex
Cortex = Bark
-
Most recent evolutionary expansion
-
~1.5-5.5 mm thick
-
6 layers of cells
-
Convoluted and wrinkled -> maximize surface area
Gyri/gyrus: bump, protruding rounded surfaces (folds)
○
Sulci/sulcus: valley b/w gyri
○
Fissure: very deep sulcus
○
-
Separated into 2 halves but can communicates
Corpus callosum ( white matter tract)
○
Anterior commissure
Connected temporal lobes
§
○
○
-
The important lobes and sulci
Frontal lobe
-
Temporal lobe
-
Parietal lobe
-
Occipital lobe
-
Insula
Buried deep within the lateral sulcus (in b/w temporal, frontal and parietal lobe)
-
Primary gustatory cortex (taste)
-
Also area important for disgust
Physical and moral
○
-
Central sulcus also separate the primary motor cortex (premotor) and primary
somatosensory cortex (post motor)
Primary Motor Cortex (M1)
Organization around specific attribute of physical world
Specific body area controlled by specific motor region
○
-
Distortion relative to physical world
Parts of body with fine motor control are larger (face, digits)
○
-
Mapping is upside-down
Body parts are represented inversely in cortex
○
-
Hemiplegia (often from stroke) results in paralysis on contralateral side of body
Occurs with unilateral damage to M1 and combined with damage to basal
ganglia
○
-
Primary Somatosensory Cortex (S1) -postcentral gyrus
Organization around specific attribute of physical world
Mapped based on area of body that receives tactile input (touch,
temperature, pain, etc.)
○
-
Distortion relative to physical world
Representation of body parts proportional to density of touch receptors
○
-
Mapping is represented upside-down in cortex
-
Neurotransmitters
Amino acids
Glutamate (CNS) - excitatory a.
GABA (CNS) - inhibitory b.
Aspartate (PNS)c.
Glycine (PNS)d.
1.
"System" neurotransmitters
Acetylcholine a.
Dopamineb.
Norepinephrine (noradrenaline)c.
Serotonin d.
2.
Effects of many neurotransmitters depends upon the receptor subtype they bind to
Amino acids (CNS)
Glutamate Gamma-aminobutyric acid (GABA)
Excitatory
-
Plays role in epilepsy
-
Excess causes
cytotoxicity
-
Precursor to GABA
-
Inhibitory
-
Two kinds of receptors
GABA A (ionotropic) - ion channel•
GABA B (metabotropic) - G couple receptor protein•
-
Activation results in sedation and sleep
Alcohol activates GABA•
Brain becomes overactive, can’t downgrade the
activity, could die
•
-
Anxiolytics and Benzodiazepines (i.e. Xanax) activate GABA
-
Neurotransmitters systems
Acetylcholine
-
Monoamines:
Dopamine
○
Norepinephrine (noradrenaline)
○
Serotonin (from tryptophan)
○
-
Cholinergic system: Acetylcholine (Ach)
2 main receptor subtypes:
Nicotinic (ionotropic)
○
Muscarinic (metabotropic)
○
-
Nuclei in pons, midbrain and basal forebrain
-
Maintains cortical excitability, decreases with anaesthesia
-
Selective attention ( filter out distractive info)
-
Motivation & reward
-
Dopaminergic system: Dopamine (DA)
3 subsytems:
Nigrostriatal (substantia nigra)
Movement - Parkinson's
§
○
Mesolimbic (VTA) - main dopamine producer
Prediction error, reward, motivation
§
○
Mesocortical (VTA)
Working memory
§
○
-
2 main receptor subtype families
D1 (excitatory)
○
D2 (inhibitory)
○
-
Noradrenergic system: Norepinephrine (NE)
Nuclei in Locus Coeruleus
-
Mobilizing the brain by enhancing sensory processing
-
Role in arousal and attention
Shuts off during REM sleep
○
-
Also main NT for sympathetic nervous system
Fight or flight response
○
-
Vessel constrictor: AP pen, shot in epinephrine, increase BP
-
Serotonergic system: Serotonin (5-HT)
Main source in Raphe Nuclei in brain stem
-
Controls transmission of dopamine and epinephrine
-
Many effects
Arousal, mood, anxiety
○
Eating
○
Pain
○
Sexual behaviours
○
Memory
○
-
Putative (uncertain) role in depression
Selective serotonin reuptake inhibitors (SSRIs)
Works immediately, but the actual effects takes weeks
§
○
-
Methods in Cognitive Neuroscience
Lesion method 1.
Brain imaging
Electrical/magnetic
EEGi.
MEG ii.
Single cell iii.
a.
Metabolic
fMRIi.
PETii.
EROS iii.
b.
2.
Brain lesion method: Neuropsychology
IF: function X is disrupted by lesion to brain region Y
-
THEN: brain region Y supports function X
-
Suggests a causal link b/w region and cognitive function
-
Patient Gage
-
Two conceptual approaches
What function is supported by a given
brain region?
What brain region supports a given cognitive
function?
Examine a group of patients with similar
lesions
-
Compare to a control group of patients
with different lesions
-
Examine a group of patients with similar
cognitive impairment
-
Then examine the brain regions common
with deficit
-
Human and non-human lesion studies
Human neuropsychology Non-human neuropsychology
Acquired brain damage
Naturally occurring neurological
condition or surgical treatment of
condition
-
Not under control of experimenter
Location and extend of lesion,
demographics
-
Single-case or group studies
Under control of experimenter
Lesion location and size, sample,
environment, age
-
Precise brain structures selected for
lesioning
Using surgical and neurotoxic
procedures (permanent or reversible
lesions)
-
Double Dissociation
Determine whether two functions are independent
Patient with damage to area X has impaired function A, but function B is fine
○
Patient with damage to area Y has impaired function B, but function A is fine
○
-
Example:
lesion to Broca's area (X) impairs speech production (A) but not
comprehension (B)
○
Lesion to Wernicke's area (Y) impairs comprehension (B) but not production
(A)
○
-
Brain Lesion Study Limitations
Disconnection syndrome: area X may not participate directly in function A but may
disconnect two critical brain regions that are critical for function A
E.g. split-brain patients
Serving the fibers of the corpus callosum leads to certain cognitive
impairments
§
But it’s not the corpus callosum that carries out these functions!
§
○
-
Lateralization of language
For the majority of people language centers are located in left hemisphere
-
In split brain patients the left and right hemispheres cannot communicate
-
The visual system is contralaterally organized
So images presented in left visual field are represented neural in right
hemisphere
For split brain, present stuff at left VF -> right hemisphere -> cannot
verbally say the item but can point towards the item.
§
○
-
Sitting on a 2 legged stool
Function may be unrelated to area X but actually related to the brain with area X
intact
-
Ascribe non-functionality to broken leg: infer that specific leg is necessary for
functioning of stool
Wrong! All legs participate
○
Stool failure is result of system level dysfunction
○
-
Brain involves 100 billion interconnected neurons
Relies on both localization of function and distributed processing!
○
Also compensatory reorganization occurs!
○
-
Brain imaging
Anatomical/structure imaging
CT, MRI
○
-
Functional/dynamic: physiological imaging
Access how neural activity varies over time
Electrical
Intracranial and/or scalp EEG, ERP □
§
Metabolic
PET, fMRI □
§
○
-
Functional brain imaging: EEG(electroencephalogram)
Measures voltage fluctuations from electrical signals of neuron populations
-
Electrodes measure underlying electrical activity through the scalp
-
Difference b/w designated reference (i.e. earlobe, mastoid) and recording
electrodes produces and electrical potential
-
Sums activity from all over the brain
Great temporal solution
○
-
Depicts time course of global brain activation
-
Event-related potentials (ERPs) are a special case of EEG: brief changes in signal
Average EEG signal from many trials
○
Lock the signal to the onset of stimulus or a motor response and you get ERP
Large background oscillations of the EEG signal make ERP detection
from single trial impossible
§
Need to average hundreds of trials -> remove EEG background, reveal
ERP
§
○
Many different kinds of ERPs with different signatures and associated with
different cognitive functions
○
-
Pros Cons
Good temporal resolution
-
ERPs can tell us about cognitive processes
-
Much more affordable than MRI/fMRI
-
Poor spatial resolution
-
Cannot access deep brain structures (e.g.
medial temporal lobe)
-
Functional brain imaging: MEG
Records magnetic fields generated by electrical currents using SQUID arrays
(superconducting quantum interference devices)
-
Great temporal and spatial resolution
-
Magnetic fields are less distorted by skull, scalp and movement interference
-
MEG is sensitive to neocortical activity
Epilepsy and neurosurgery localization
○
Often paired with fMRI
○
-
Structural brain imaging: CT scans (computerized axial tomography)
First modern technique before MRI
-
Allows for localization of brain damage
-
Utilizes X-rays for visualization
-
Different tissues have different desnsities
X-rays (sub-par spatial resolution) pass easily through low-densities (water,
ventriculus fluid, blood) but are absorbed by high-densities like bone
Density gradient
the darker it is the less dense it is□
Black -> White
CSF < brain tissue < blood < bone
®
□
§
○
-
Structure brain imaging: MRI (Magnetic Resonance Imaging)
Quest for better resolution and more brain coverage requires a very strong magnet!
1 Tesla (T) = 10,000 Gauss
○
Earth's magnetic field = 0.5 Gauss
○
4T magnet is 80,000 times the strength of the Earth's magnetic field
○
A lot of helium
○
-
Uses a large magnet measure in Tesla (field strength)
-
Combined with radio frequency pulse of a specific resonance
-
This creates an image
Many organic elements in the body are magnetic
Hydrogen: most abundant in the body
§
Protons spin around a random axis
§
○
When placed inside a magnetic field the protons all become aligned in parallel
○
A radio frequency (RF) pulse sequence is used to push protons put of
alignment with the magnetic field
○
The time it takes for the protons to revert back to original orientation is
measured through the head coil
○
Protons relax at different rates in different tissues which produces a
gradient that reconstructed as a image
○
-
Advantages of MRI over CT
No x-rays
○
Superior spatial resolution
○
-
MRI vs. fMRI
High resolution (1mm)
§
One image
§
2D slices of the brain
§
○
-
fMRI
Neurons get O2 via hemoglobin in RBC
-
When neuronal activity increases O2 demand increases, so more blood flow
-
Oxygenated blood is diamagnetic (magnetically repelled) and paramagnetic when
deoxygenated (magnetically attracted)
These differences in oxygenation and their magnetic properties create
differences in MR signal, which can be used to infer brain activity
○
-
This is known as blood oxygenation level dependent (BOLD) imaging
-
Hemodynamic response
Hemodynamic response (HR) is change in regional cerebral blood flow (rCBF)
over time
○
Neural response to stimulus happens in ms
○
HR peaks 5-10 sec post stimulus (SLOW)
Starts about 2s after stimulus presentation
§
○
Experimental design
Block designs
Examine extended HR across same trial type
§
○
Event-related designs
HR for different, individual trials
§
Allows examination of trial specific HR, such as predicting memory later
on from HR
§
○
Subtractive logic
fMRI detects a change in signal form one condition to another - therefore you
must always contrast 2 conditions
○
Functional images are subtracted from one another
○
Superimposed on anatomical image
○
Importance of well-designed baseline!
Depend on your questions: e.g. all regions specific to viewing a face or
all regions involved in viewing a face
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PROS CONS
Non-invasive, no radiation
-
Can do multiple scans with same person
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Great spatial and good temporal resolution
-
People love images
-
Very expensive
-
Correlational
-
People love images
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Positron Emission Tomography (PET)
Measures local changes in cerebral blood flow (rCBF)
-
Measures rCBF over a few minute period (doesn't have the best temporal)
-
Radioactive isotopes tracers introduced into the body
Isotopes rapidly decay -> this decay is measured to produce the signal
○
-
PROS CONS
Track multiple metabolic processes
Specific NT can be labeled and
measured (isotopes tag to specific NT
receptor sites)
•
-Invasive: radioactive isotopes
Can only be administered limited
number of times
•
-
Highly limited temporal resolution
Limited by the half life of the
isotope used
Oxygen-15 gives an image of
brain activity averaged over
1.5 mins; fMRI average over
2s
○
•
-
Diffusion Tensor Imaging (DTI)
3D modelling technique that shows neuroanatomical connectivity by measuring
tissue bundles
-
Tractography maps show white matter connectivity via water flow measurements
in tissue
-
Looking at neurodegeneration
-
Transcranial Magnetic Stimulation (TMS)
Localized magnetic pulses alter electrical activity of neurons
-
TMS coils can activate or deactivate a region of neurons
-
Determining causation
○Brain region A appears to be active in decision-making task (fMRI evidence)
○Administer TMS to region A and to different brain region B (control area) not
involved in decision making task. See how performance differs
○If TMS on region A influences task, but TMS on region B does not, shows
evidence suggesting region A is causally linked to the mental process engaged
by task.
-
Optic imaging
-Laser of infrared light
-Sensors detect distortions in light
-Great temporal and spatial resolution
-Drawback is only cortical activity can be detected
Reflexive: involuntary
Foveation: voluntary or involuntary
Central (Rolandic) sulcus: separate frontal and parietal
Sylvian (lateral) sulcus: separate temporal from frontal
and parietal
Agonist: a chemical binds to
receptor and mimics effects of
the neurotransmitter
Antagonist: a chemical that binds
to receptor and inhibits or block
effect of the neurotransmitter
Catecholamines (from tyrosine)
Low resolution
-
Many images / 2 s
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Lecture 2
Thursday, May 24, 2018 3:51 PM
Document Summary
A pioneer in electrophysiology of single cell recordings. Phenology (pseudoscience): areas that are more used will be bigger - the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life. Brain cavities filled with spinal fluid (shock absorber) Brain stem contains many ancient structures responsible for vital functions. Contains nuclei of cranial nerves (9-12) involved in facial motor and sensory signals. Most motor fibers are contralaterally organized in the medulla. They cross from one side of the body to the other. Controls vital functions such as breathing and heart rate and reflexes. Also contains set of neurons that make up the reticular activation system. Lies below the midbrain, above the medulla and in front of cerebellum. Many diverse functions including facial sensation, movements, saliva, tear secretion and vestibular function (balance) Includes the superior olive, a major relay hub for transmission of auditory input from ear to brain.
