Neuroscience Lecture 6 2024.pdf

Neuroscience Lecture 6 Lateralisation of function and split brains Memory Carlson pp 114-115  Hemispheric Lateralisation: Differences between the hemispheres Body and sensory world split between two...

Neuroscience Lecture 6 Lateralisation of function and split brains Memory Carlson pp 114-115  Hemispheric Lateralisation: Differences between the hemispheres Body and sensory world split between two cerebral hemispheres: right hemisphere receives sensory input from left; and controls motor response on left side of body Sensory left hemisphere receives sensory input inputs from right; and controls motor Motor response on right side of body. outputs  Hemispheric “Dominance” Several “higher” functions are lateralised. One side is more important (“dominant”). Eg, hand-preference indicates superiority of one hemisphere for manual control.  Hemispheric “Dominance” Of all cognitive or behavioural functions, language is the most strongly lateralised: for most of us, the left hemisphere controls speech and is better at comprehension Lateralisation of language Evidence: Aphasia after a stroke Brain imaging: dichotic listening task: people understand a word faster if presented to right ear  Speech Areas Broca’s Area Lower posterior region of left frontal lobe Damage to Broca’s Area causes difficulties speaking (“expressive aphasia” or “non- fluent aphasia”), but generally can understand speech (except grammatically complex sentences). Broca’s aphasia is not just motor problem, because often can sing. Problems with writing but not drawing. Deaf signers can lose ability to sign.  Speech Areas Wernicke’s Area Posterior region of left temporal lobe Damage to Wernicke’s Area causes problems with comprehension of speech (“receptive aphasia”). Produce fluent but meaningless speech (“fluent aphasia”) Cannot read.  The Split Brain Lateralisation of function not normally evident because info shared between hemispheres by corpus callosum But some patients with intractable epilepsy had surgery to cut the corpus callosum (“callosotomy”)  split brain patients  The Split Brain Split brain patients can still walk, talk, suffer little or no impairments of intelligence or emotion. But did report some disquieting difference between what left and right hands did (e.g., choosing clothes) Roger Sperry extensively studied split brain patients  The Split Brain Sperry found that patient could name an object put in his/her right hand, but not if object put in left hand. apple banana Naming a word flashed on left vs right side of screen. Or, 2 words flashed on screen, and patient has to find the objects hidden behind screen. banana apple  Functions in right hemisphere Early idea that right was submissive to left But right brain can comprehend simple language Seems right brain contributes more than left to adding and interpreting emotional content in speech (eg, sarcasm)  The Hippocampus Best recognised memory structure in brain.  Memory & The Hippocampus Case of Henry Molaison (“HM”): Had brain surgery to treat intractable epilepsy (26 y.o.), surgeon removed hippocampus on both sides (+amygdalae and some surrounding cortex) surgery worked as treatment for epilepsy, but rendered HM unable to learn and remember new information (dense amnesia)  Hippocampal Amnesia Brenda Milner studied HM for many years. HM’s older memories, acquired before the lesion, were spared. Now shown in many patients that damage to the hippocampus causes severe anterograde amnesia (can remember old stuff but can’t learn anything new) Deficit only in creating new long-term memories, as patients with hippocampal damage can retain new information in short-term memory.  hippocampus is not where memories are “stored”.  Hippocampal Amnesia Deficit specific to declarative learning and memory.  patients like HM show normal procedural learning, even though they can’t recall having done task before  Wernicke-Korsakoff’s Syndrome Amnesia not only due to brain damage, but also diseases. Severe deficiency in vitamin B1 (thiamine) in chronic alcoholics (alcohol interferes with B1 absorption) triggers Wernicke Encephalopathy (confusion, and disordered gait and eye movements). Untreated, WE leads to Korsakoff’s Psychosis, characterised by profound anterograde amnesia and some retrograde amnesia (+ confabulation). Amnesia due to irreversible damage to mammillary bodies (part of hypothalamus) and part of thalamus. Mammillary body  Alzheimer’s Disease Progressive degenerative disease characterised by: Loss of newly learned information, followed by loss of distant memories, factual knowledge, and finally procedural skills. Widespread neuro-degeneration in brain brain actually shrinks (sulci and ventricles enlarge)  Alzheimer’s Disease Abnormal neural tissue present in brain: especially prevalent in cortex and hippocampus senile plaques Neuro-fibrillary tangles