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Chapter 2b Neurocognition

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PSYC 221
Thomas Spalek

Neurocognition 1 Terminal button attaches to dendrites of neighbouring neurons Types of Neurons 1. Sensory neuron aka afferent neuron – from the external environment to the CNS 2. Motor aka efferent neuron – project away from CNS to muscles 3. Interneuron – form bridges between sensory and motor neurons (important component of the reflex arc) 4. Pyramidal neuron – in the cortex – PRIMARY NEURONS ASSOCIATED WITH COGNITION Nerve Communication 1. Polar – it has a positive and a negative end (e.g., a battery) (average = -70 mV) 2. Depolarize 3. Hyperpolarize (re-polarize) 4. Refractory period - keeps AP from only going one direction down the axon • Excitatory neurotransmitters like acetylcholine • Inhibitory neurotransmitters like GABA • If a target neuron is sufficiently excited  will produce an AP  transmit it’s NT to the next neuron • AP is an all-or-none response that is always the same magnitude UNLIKE POST- SYNAPTIC POTENTIALS Anatomy of the Brain • Central fissure goes from the top middle of the brain and extends all the way down the side to the ear • Corpus callosum = broad band of nerve fibres connecting the two hemispheres of the brain • White matter = myelinated portion of neurons in the brain; more dense • Gray matter = cell bodies in the brain Neurocognition 2 Structural Techniques • Lesions/brain damage • Virtual lesions – Transcranial magnetic stimulation (TMS) ○ Create “virtual lesions” with electrical coils with a magnetic field aiming towards scalp, overstimulating small areas in the brain which creates temporary lesions that can help neuro research • Wilder Penfield – neurosurgeon in Canada, mainly Montreal ○ Famous for brain surgery on epileptic patients ○ Direct stimulation – stimulate areas before getting rid of epileptic areas in surgery while the patient was awake – some patients even smelled burnt toast ○ Mapped brain areas using direct stimulation that are still used today with almost no change despite being created 70 years ago ○ Single cell recordings – plant recording device in cell, manipulate stimuli to record the cell’s response to that stimuli CT/CAT – Computer Axial Tomography • Uses x-rays shot at different angles, working in unison with x-ray detectors, to get a picture of what’s inside body • Measures amount of x-rays absorbed by your head ○ Different tissues absorb x-rays at varying degrees • Computer analyzes intensity of the x-rays as they leave the body and produces a picture Magnetic Resonance Imaging • Large magnetic field ○ Earth magnetic field = .000005 Tesla ○ MRI = 4 Tesla ○ That is 800,000 times greater • Radio wave pulses shot at head Neurocognition 3 • Different tissues transmit radio waves BACK to the sensors • These waves are analyzed and turned into images • Hydrogen = most abundant atom in the body • The hydrogen proton spins/wobbles in a magnetic field • MRI magnet causes axes to align with the external magnetic field ○ Precession (the “wobble”) is still random • The radio frequency (RF) pulse makes the protons “wobble” together ○ Remember the TA waving his arms around like he’s dancing • When the RF pulse is turned off, the protons return to their random state • They release energy in the form of radio waves • Different tissues release energy at different rates • These waves are analyzed by a computer, and a picture is created CT vs. MRI Advantages of MRI over CT • Higher resolution; better visualization of brain • No radiation Advantages of CT over MRI • More comfortable environment • No danger of foreign materials in body or MRI room Functional Techniques EEG – Electroencephalography • Electrodes measure rapid post-synaptic potential changes of pyramidal cells in cortex (NOT AP’s) Event-related potentials (ERP’s) • Electrical fluctuations time-locked to a specific event Friedman and Trott (2000) • ERP’s for studied words • Find higher activation for HITS than MISSES • Source analysis points to the Left Prefrontal area as being important to encoding words Advantages of ERP’s • High temporal resolution = very fast = not even a third of a second • Non-invasive = just put on an EEG cap • Relatively inexpensive Disadvantages of ERP’s • Low spatial resolution • Requires MANY trials (like 1000) • Not too comfortable (i.e., must minimize muscle movement and blinking) PET – Positron Emission Tomography Neurocognition
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