PSYCH 1XX3 Final: Neuroscience II
14 Jul 2018
School
Department
Course
Professor
Neuroscience II
Terminology
• Neuraxis – line along spinal cord, through to the front of the brain
o Because of the curve in the neuraxis, at the level of the head dorsal is up, and at the level
of the spinal cord it is the back
o This line bends forward as the spine enters the brain
o Rostral – towards the head (towards the top of the axis)
o Caudal – towards the bottom of the axis
• Dorsal – refers to the back of the axis
• Ventral – to the front of the axis
• Medial – structures that are closer to the centre of the brain
• Lateral – structures that are farther away from the centre of the brain
• Ex. The rostral ventral medial medulla (towards the top, in front of the neuraxis, towards the
midline of the brain)
Studying the Brain
• Franz Joseph Gall’s phrenology theory – different brain functions were in different areas (no
scientific evidence)
• Different mental attributes (ex. Benevolence, hope, intelligence) were in different sub-organs of
the brain and these sub-organs would grow with the use of that facility
• Growth could be measured by looking at the shape of the skull (not true and the theory was
dismissed)
Lesion Studies
• If part of the brain is damaged/removed, and a function is lost, then that structure is associated
with that function
• Pierre Florens conducted ablation studies (studies that remove parts of animal’s brains) on
pigeons
o Removal of cerebellum affected motor coordination, removal of medulla affected heart
beat & respiration
• In humans, patients with accidental brain damage are examined to determine the site of the brain
damage (done during autopsy after death) and their functional change in behaviour
• Lesion studies must be specific to target the function of a brain region
• Phineas Gage - railroad man survived an iron rod being driven through his head, destroying his
left frontal lobe
o Before he was capable and efficient, and after he was fitful, irreverent, profane, didn’t
care about others, could not plan future actions, and was constantly changing ideas
o This suggested that the frontal lobes were responsible for functions like planning and
impulse control
• Brain injury links brain anatomy with behavioural deficits
• Our brain is highly interconnected so 1 lesion can affect a variety of behaviours
• Human lesion studies disadvantage – hard to target regions and draw conclusions (so we use
animals)
• Human lesion studies advantage – a direct measure of a brain structure’s function
• Lesion studies rely on autopsies after death to determine the type of brain damage, but this has a
lot of drawbacks:
o A patient may live for many years, relatives refuse to give permission of an autopsy after
death
Electrical Stimulation and Single Cell Recording
• Stimulating a part of the brain and observing the result on behavior to build an anatomical map
related to function
• Wilder Penfield did surgery (Montreal procedure) on epileptic patients to remove the focus of
epileptic activity
o The brain does not have pain receptors, so a patient going through surgery under local
anesthesia could be conscious and work with Penfield to probe the exposed brain to
locate and remove scarred tissue
o He used a thin, wire carrying a small electric charge to stimulate the cortex which leads
individual neurons to fire and he could accurately map perceptual processes and
behaviours to specific regions
▪ Ex. A patient reported seeing flashes of light if the visual cortex was stimulated
o He avoided damaging the eloquent cortex which caused paralysis, loss of language or
sensory processing
Single Cell Recording
• Electrodes can be used to record ongoing electrical activity in the brain through single cell
recording techniques
• A small electrode is inserted into the nervous tissue of an animal with its tip held outside the cell
body of a neuron
• From this electrode, neural activity is recorded while the animal performs a task or a stimulus is
presented
• The pattern of firing reveal’s a neuron’s functional role
o Ex. Hubel and Wiesel presented cats w/ specific visual stimuli while recording from
single cells in the visual cortex, and by this, cell types were identified that responded to
specific categories of visual stimuli
• Intracellular Recordings – responses recorded by these are known as single-unit recordings
o They can be inserted through the membrane with causing damage (microelectrodes)
• Extracellular Recordings – groups of larger electrodes may be inserted into the tissue
o The recorded action potentials are processed by a computer from any cell bodies near the
electrode tip
• Place cells – single cells discovered in the hippocampus of rats while recording the activity when
they wandered
o Some cells fired only when the rat was in a certain area of the cage (ex. door, food dish)
o A cognitive map of the environment is in the hippocampus of the rat
Structural Neuroimaging - X-Ray CT
• Non-invasive procedures (no surgery to open the skull) are preferred to study the structure of the
brain
• X-ray computed tomography (CT) – head is put in a ring w/ an x-ray emitter and detector on
opposite sides
• The ring rotates while the emitter passes x-rays through the head to the detector
• The detector’s responses are recorded from all angles through the head and a computer
reconstructs a brain image
• This technique helps distinguish bw tissue types, show areas of damage due to stroke, brain
injuries
• Cannot show tumours unless they are big enough to distort the underlying structure of the brain
• CT scans subject individuals to high radiation and poses a risk of cancer, pics are low resolution
so fine brain anatomy cannot be seen
• X-ray slices of the brain are taken and pieced together to make a quick and inexpensive pic of the
brain
Structural Neuroimaging - MRI
• Head is put in a large ring and strong magnetic fields image the brain
• The magnetic fields align the H atoms in the brain which can cause MRI to localize tissue
precisely (high res.)
• Tissue that is placed in a strong magnetic field, and is excited by a radio frequency pulse will
cause the body molecules to vibrate at a certain rate and emit their own radio frequency waves
• A head coil antenna detects these waves and records them for analysis
• Different molecules will produce different radio waves and the computer will decode and produce
detailed pics
• Can determine the difference bw tissue types (ex. Grey and white matter)
Functional Neuroimaging - Positron Emission Tomography
• Non-invasive techniques can be used to determine the function of various parts of the brain
• When an area is active, the corresponding neurons fire action potentials at an elevated rate (need
more energy)
o If we measure the glucose consumed at an area, we would know how active it is
• Positron Emission Tomography (PET) – when a neuron fires an action potential, energy is needed
to pump the excess Na+ back out/ create new vesicles of neurotransmitters to replace the used
ones/ remove excess neurotransmitters from the synaptic cleft (how brain function relates to
cognitive tasks like language and memory)
o Patients are injected with a mild radioactive form of glucose or oxygen (radionuclide) -
an isotope with a very short half-life (half the radioactive particles will decay back into
non-radioactive form in less time)
o Each time a radioactive particle decays, it emits 2 positrons that shoot out in opposite
directions
o A ring of detectors around the head detects positrons and a computer finds the location of
the emission
o This gives an image of the amount of brain activity in an area and overlaid with the MRI
image
• Disadvantages of PET are it is expensive to produce radionuclides, requires an atomic particle
accelerator, must be used immediately as the half-life is short, radionuclide must be injected into
an artery (invasive), patient is exposed to radiation and this poses a cancer risk, all areas are a
little active all the time and would emit particles
Functional Neuroimaging – Functional MRI (FMRI)
• Another requirement of a highly active neuron is oxygen which is carried into the area via blood
from the lungs
Document Summary
The rostral ventral medial medulla (towards the top, in front of the neuraxis, towards the midline of the brain) Studying the brain: franz joseph gall"s phrenology theory different brain functions were in different areas (no scientific evidence, different mental attributes (ex. A patient reported seeing flashes of light if the visual cortex was stimulated: he avoided damaging the eloquent cortex which caused paralysis, loss of language or sensory processing. Hubel and wiesel presented cats w/ specific visual stimuli while recording from single cells in the visual cortex, and by this, cell types were identified that responded to specific categories of visual stimuli. Functional neuroimaging electroencephalogram or eeg: when a neuron fires an action potential, some electrical current can be measured from the outside of the cell. N170 wave is a marker corresponds to face processing: this technique is not as precise as the fmri but is less expensive, and can measure short brain responses.
