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Neuroscience 2 brain structure.docx

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Department
Psychology
Course
PSYCH 1X03
Professor
Joe Kim
Semester
Winter

Description
Neuroscience 2 Brain Structure - Module 1: The Structure of the Brain o Terminology:  Dorsal = back (but is also top of head b/c of curvature of axis)  Ventral = front  Rostral= top of axis (forehead/face)  Caudal = bottom of axis, (feet)  Medial= Towards center/midline  Lateral = towards outside of brain - Module 2; Studying the Brain o Most invasive research comes from work with animals, issues or more reduced preparations o Neuroscientists have been interested in case studies of accidental brain injury which can link anatomy with associated cognitive and behavioural deficits that are observed  E.g. Phineas Gage (1848), foreman in charge of explosives to remove large sections of rock from path of railroad. Was athletic, intelligent, and full of life, respected and likeable fellow. Tragic accident = 3 foot iron rod completely through left cheekbone and through top of skull. Remarkably survived and except for some loss of vision and facial disfiguration recovered completely. Friends could not recognize him as gage they one knew, once upbeat, polite and caring person, Gage became prone to selfish behavior and bursts of profanity. He became erratic and unreliable and had trouble forming and following through on plans. Gage’s case provided support for the view that the brain has specializes structures for complex behaviours.  Advantage of Case Studies:  A direct measure of a brain structure’s function  Disadvantage  Hard to selectively target particular regions (rarely isolated damage) and draw conclusions that are specific enough to be useful  Disadvantage can be overcome by studying brain lesions induced in animal models. In such ablation studies, a researcher destroys, removes, or inactivates a defined brain region and observes the result on behaviour. The accuracy of this emerging understanding of structure and function can depend on the precision of the lesion. Even so, because the brain is highly interconnected, often a variety of behaviours are affected by a single lesion. o An alternative approach to lesioning is to electrically stimulate an area of the brain and observe the result on behaviour to build an anatomical map related to function. (used extensively by Canadian neurologist Penfield as he performed brain surgery to treat patients w/ severe epileptic seizures)  He revolutionized techniques in brain surgery as he perfected his “Montreal procedure” to treat patients experiencing severe seizures. In doing so, he had to be sure that critical areas of the brain were left intact. B/c the brain itself does not have pain receptors, a patient undergoing surgery could be under local anaesthetic and fully conscious, working with Penfield to probe the exposed brain to locate an remove the scarred tissue that caused seizures. Penfield used a thin wire carrying a small electric charge to stimulate to cortex. This stimulation lead individual neurons to fire, and thus Penfield could very accurately map perceptual processes and behaviours to specific brain regions.  E.g. if area of visual cortex stimulated, patient reputed seeing flashes of light and if an area of the motor cortex was stimulated, a patient would experience a muscle twitch. o Electrodes can also 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 a live animal model with its tip held just outside the cell body of an individual neuron. From this electrode, neural activity is recorded while the animal performs a task or a stimulus is presented. The pattern of firing reveals a particular neurons role. (E.g. if neuron in cat brain fires only if small vertical bars presented, then you know that function of neuron has to do with small vertical bars.) o To study large-scale structure and function of brain regions, neuroscientists use structural and functional neuroimaging techniques. o Structural Neuroimaging:  Computed Tomography (CT)  During a CT scan, a series of X-ray slices of the brain are taken and pieced together to produce a relatively quick and inexpensive picture of the brain  These scans are often helpful to diagnose brain injuries  Limitation by today’s standards: o Relatively low resolution = difficult to examine fine brain anatomy with a CT scan and so not often used in neuroscience research.  Magnetic Resonance Imaging  In a MRI machine, powerful magnetic fields are generated which align the hydrogen atoms found throughout the brain, while these atoms are aligned, an MRI can be used to localize tissue very precisely throughout the brain.  Provides a detailed structural image of the brain o Functional Imaging Techniques  Used to learn how brain function relates to cognitive tasks such as language and memory.  Positron Emission Tomography  A radioactive tracer of glucose or oxygen is injected into the bloodstream. The radioactive molecules make their way to the brain and are used in metabolic processes which are detected by the PET scan.  The logic is that more active brain areas will use more metabolic resources, and so an image of the brain’s relative pattern of activity can be constructed.  Disadvantage: o Requires radioactive tracer to be injected – fairly invasive.  Functional magnetic resonance imaging (fMRI)  Often preferred b/c it can produce a relatively clear image of the brain’s activity w/out the need for a radioactive tracer.  Works by measuring the blood oxygen dependent signal, and uses many of the same principles as the MRI  It is able to measure the relative use of oxygen throughout the brain and operates under the same basic assumption as the PET scan – more active areas of the brain require more metabolic resources  Limitations: o fMRI provides only very rough image of brain activation o Oxygen use by the brain often spikes a few seconds later that the spikes of activity in the brain – and a few seconds can be a very long time in terms of brain functions  It is not the best method to use if researcher is interested in the precise timing of brain activation and function.  Electroencephalogram (EEG)  The electrical activity of the brain can be recorded through the scalp by wearing a cap of very sensitive electrodes.  Limitations: The EEG provides only a very rough image of the brain’s overall activity, from populations of neurons.  However, with a few clever modifications, the EEG can become more informative o In an event related potential (ERP) experiment, a specific stimulus is presented to the subject repeatedly while the EED is recording. Although the EEG will generally produce very noisy waves, the specific stimulus presented can have a small and consistent effect on the readout. By averaging the EEG signal across many trials, the noise can be balanced out, and what remains is a characteristic signal. These ERP signals can still be difficult to interpret, but there are a number of reliable signals reported throughout the literature that serve as markers for different types of neural processes. E.g. 1 such marker, called the N170 wave, which is thought to correspond to face processing  When combined w/ a behavioral measure, EEG and ERP signals can be highly informative markers, with very precise temporal resolution on the order of milliseconds. - Module 3: The Brain Regions – Hindbrain o All information into and out of the brain travels through cranial nerves or through the spinal cord, which connects to the hindbrain at the very base of the brain. o Structures of the hindbrain are evolutionarily the oldest parts of the brain and found in some form in nearly every vertebrate species. They are primarily involved in he regulation of vital body functions. o Medulla  Most caudal part of the hindbrain and lies directly above he spinal cord  Structurally looks like extension of spinal ford  Plays an important role in vital functions such as breathing, digestion and regulation of heart rate o Pons  Small structure rostral of medulla  Relays information about movement from the cerebral hemispheres to the cerebellum.  Processes some auditory information and is thought to be involved in some aspects of emotional processing  Contains a number of nuclei that area generally part of the reticular formation o Reticular Formation  Set of Interconnected nuclei found throughout the hindbrain (excluding the cerebellum). Has two main components:  Ascending Reticular Formation (reticular activating system (RAS))  Primarily involved in arousal and motivation and may be a large part of a large network responsible for your conscious experience.  Important roles in circadian rhythms  Damage to RAS lead to devastating losses in brain function and in the extreme case permanent coma  Descending Reticular Formation  Involved in posture and Equilibrium  Plays important role in motor movement o Cerebellum (little brain)  Resembles miniature version of entire brain  Coordinates all movement – motor commands pass through the cerebellum as they signal muscles to contract, and during production of movement, sensory signals return to the cerebellum for immediate error correction.  Patients with Damage – display exaggerated, jerky movements overshooting or missing targets completely  - Module 4: The Brain Regions – Midbrain o Relatively small regions with two major subdivisions: o Tectum  Located in the dorsal portion of the midbrain and contains 2 primary structures related to perception and action:  Superior Colliculus – involved in eye movement and reflexes (+ receives visual input)  Inferior Colliculus- involved in auditory integration (+receives auditory input) Tagmentum o Tegmentum  Contains important structures  Nuclei of the reticular formation  The Red Nucleus o Important structure involved in the production of movement o In vertebrates with less complex brains, is the most important structure for the regulation and production of movement as it projects directly to the cerebellum and spinal cord. o In humans, red nucleus plays lesser role as relay station for information from higher motor areas to and from the cerebellum and spinal cord. o However in young infants with still developing brains, many motor behaviours may still be controlled by the red nucleus  The Substantia Nigra
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