Higher Cortical Functions & Cognitive/Behavioral Manifestations of Brain Disorders (Continued) PDF

Higher Cortical Functions & Cognitive / Behavioral Manifestations of Brain Disorders (continued)  Examples of “Higher-Order” Functions Language Memory Executive Functions Perception Spatial Behaviour Attention Skilled Movement  Percep...

Higher Cortical Functions & Cognitive / Behavioral Manifestations of Brain Disorders (continued)  Examples of “Higher-Order” Functions Language Memory Executive Functions Perception Spatial Behaviour Attention Skilled Movement  Perception Refers to cognition resulting from the activity of the various sensory regions of the cortex beyond the primary sensory cortex  Central Organization of PrimarySensory to Systems Secondary Secondary areas perform perceptual functions Modality specific Tertiary areas are not sensory specific  Agnosias Refers to partial or complete inability to recognize sensory stimuli Typically affect a single sensory system (e.g., vision, audition, tactile) Not explained by a defect in primary sensory processes or reduced alertness  Example: Visual Associative Agnosia Difficulty recognizing objects visually despite intact vision (i.e., shape, size, colour of objects are seen) Patients are able to describe visual features, copy and match objects May affect selected class of items (e.g., face agnosia = prosopagnosia) Usually results from occipital and/or posterior temporal damage, often bilateral  Spatial Behaviour All behaviours with which we guide our bodies through space Ability to move from one place to another from memory = topographic memory Mental representations of space = cognitive maps Right-hemisphere plays special role Spatial impairments typically result from RH damage  Attention Refers to processes that either allow a selective awareness of an aspect of the sensory environment or allow selective responsiveness to one class of stimuli (Kolb & Whishaw) Variety of types (e.g., selective, divided) May be specific to a sensory modality Related to executive functions  Attention Subserved by diffuse neural networks involving brainstem (RAS), sensory regions, parietal, cingulate and prefrontal cortex Affected by many neurologic disorders (esp. TBI) Deficits are typically bilateral Deficit that is especially severe on one side of space = hemi-inattention or sensory neglect  Sensory Neglect Characterized by a failure to report, or respond, or attend to, stimuli on the side of body opposite to lesion, despite adequate sensory and motor function May manifest in any modality (i.e., visual, auditory, somatosensory) Often accompanied by anosoagnosia Usually results from right parietal damage, causing left-sided neglect  Hemianopia vs. Neglect Hemianopia is different than sensory neglect Hemianopia is a visual field defect (i.e., primary sensory disorder) Neglect is an attentional disorder Skilled Movement  Apraxia Disorder of skilled movement not caused by muscle weakness or other primary motor disturbance (target movements can be carried out in some contexts) Involves “high-level” motor functions (e.g., difficulties with goals, plans, sequences)  Example: Ideational Apraxia Difficulty undertaking a series of movements involving some ideational or planning component Individual steps may be performed Objects often used inappropriately Examples: Person tries to light a candle by striking a match on it Person tries to open a can of soup by hitting the can with the can opener Often results from diffuse bilateral lesions (e.g., in AD)  Example: Apraxia of Speech Difficulty coordinating motor sequences of sounds Usually results from LH lesions Often accompanied by Broca’s aphasia (may be difficult to distinguish) Often accompanied by other forms of apraxia Related Topics: - Cerebral Asymmetry - Plasticity Text Reading: Ch. 11, 12, 23 & 25  Cerebral Asymmetry Traditional Ideas: Left hemisphere (LH) important for: – Production and comprehension of language – Controlling movement on right side of body Right hemisphere (RH) important for: – Perceiving and synthesizing visuospatial (nonverbal) information – Controlling movement on left side of body  Evidence of Asymmetry from Neurological Patients Common Deficits After Lateralized Lesions Left Hemisphere Right Hemisphere Language (esp. Some linguistic functions production & syntax) (e.g., prosody, Verbal memory pragmatics, high-level comprehension) Visual memory Visual & spatial abilities Some music components (e.g., temporal aspects) However, it is important to note that… Laterality is relative, not absolute – Both hemispheres participate in almost every behaviour (network models) Site is as important as side – E.g., R and L frontal lobes more similar than R frontal and R occipital Individual variability (e.g., handedness, sex differences)  Variations in Cerebral Asymmetry Handedness Differences: More L-handers than R-handers have RH or bilateral representation of language “Dominant hemisphere” = hemisphere that contains language “Non-dominant hemisphere” = hemisphere that does not contain language  Variations in Cerebral Asymmetry Sex Differences: Extent of anatomical asymmetry may be greater in males than females Corpus callosum may be larger in females than males Females & males may (on average) have different cognitive strengths (F > M in some verbal, STM, perceptual detail tasks; M > F in some visual- spatial & mathematical tasks) Neuroimaging evidence for functional  Neural Plasticity Ability of brain to change as a result of experience Changes are structural (e.g., organization & size of different areas & circuits) and chemical (e.g., distribution & amount of neurotransmitters). Networks are strengthened &/or weakened.