Subcortical Regions - Basal Ganglia & Thalamus PDF

**Chapter Ten: Subcortical Regions** **Part One: Basal Ganglia and Thalamus** **Overview** - We will talk about two main structures - Basal ganglia - Thalamus **Basal Ganglia Functions** - 2 functional pathways - Direct motor pathway: pyramidal system - Voluntary motor system -...

**Chapter Ten: Subcortical Regions** **Part One: Basal Ganglia and Thalamus** **Overview** - We will talk about two main structures - Basal ganglia - Thalamus **Basal Ganglia Functions** - 2 functional pathways - Direct motor pathway: pyramidal system - Voluntary motor system - BG important in facilitating & coordination voluntary movement - Indirect motor pathway: extrapyramidal system - Involuntary motor system - BG important in inhibiting unwanted movement & dampen erratic movement, maintaining muscle tone, posture, and balance - BG also important in cognition, learning, motivation, etc. **Basal Ganglia (BG)** - The BG are clusters of cell nuclei that sit deep in the brain - Consist of subcortical grey matter (cell bodies) - Full set on the left and full set on the right - The BG require neurotransmitters (e.g., dopamine) - Neurotransmitters have an excitatory role (facilitates movement) and/or inhibitory role (inhibits movement) - Important to have this balance for smooth and precise movements; lack of balance = movement problems **Corpus Striatum in the Basal Ganglia** - Made up of the caudate nucleus + putamen - These are connected by bridges of grey matter - Critical INPUT area into BG from the cerebral cortex to - Facilitate volitional movement - Inhibit unwanted movements **Globus Pallidus & Substantia Nigra in the Basal Ganglia** - Critical output areas of the BG - Receives info from the putamen in the BG - Sends signals about movement out from the BG to the cerebral cortex and brainstem (mostly through the thalamus) to: - Facilitate volitional movement - Inhibit unwanted movements **BG: Parkinson's Disease** - Parkinson's disease results from degeneration of neurons in substantia nigra that produce dopamine - Parkinson's can be hereditary or acquired (e.g., TBI) - Signs - Too much movement: resting tremor - Too little movement: facial expression, articulators - Rapid rate of movement (e.g., speech) with reduced range of movement and reduced breath support = poor speech intelligibility **BG: Huntington Disease** - Neurons in caudate nucleus (basal ganglia) that INHIBIT movement degenerate = unwanted movements - Affects walking, speech, swallowing, etc. - Cognitive and behavioral changes due to frontal lobe damage - Genetic and runs in families **BG Speech Disorders: Apraxia** - Deficit in motor planning and programming - In corticobasal syndrome, apraxia results from loss of neurons in cortex and basal ganglia **BG Speech Disorders: Dysarthria** - Parkinson's disease -- hypokinetic dysarthria - Huntington disease -- hyperkinetic dysarthria **BG: Cognition** - Huntington disease and Parkinson's disease - Often involves cognitive decline in disease progression - Executive functions, e.g., reward-based learning, value-based decision making - Also, attention, memory, Theory of Mind, and related social pragmatic skills - Substantia nigra has cells that produce dopamine - Dopamine is a neurotransmitter - Damage in dopamine-producing cells in the substantia nigra - Results in loss of dopamine in different areas of the brain - One area is potentially affected is the prefrontal cortex - Important for cognitive functions **BG: Swallowing** - Parkinson's disease - Dysphagia, with problems in the oral stage and pharyngeal stage, is common - Requires longer time to eat - Reduced desire to eat - Problems selecting safe foods to eat - Lingual pumping: affects tongue retraction to control and propel bolus = spills into pharynx and airway before ready to swallow - Huntington Disease - Dysphagia: unwanted movements cause problems with the oral stage and pharyngeal stage, plus fear of choking - Inadequate chewing before swallowing - Food bolus too large (big bites) - Rapid rate of eating - Problems propelling bolus to pharynx - Residue in mouth or pharynx that enters airway - Breathing during the swallow (vocal folds abducted) - High risk of aspiration, and many deaths due to aspiration pneumonia **Thalamus Overview** - There is a thalamus in each cerebral hemisphere located just above the brainstem - The thalamus is made up of mostly grey matter (cell bodies) with some white matter (axons) - Each thalamus consists of a collection of nuclei that form two ovals **Thalamus Function: Relay Neural Signals From CNS** - Relay station for neural tracts from the CNS - Thalamus receives neural signals (information) from cerebral cortex -- sends to appropriate parts of the brain - Important for - Works with basal ganglia to maintain cortical arousal - Cortical arousal -- increase in the wakefulness, vigilance, heart rate, ventilation, and muscle tone = body gets activated physiologically to respond to stimulus (internal or external) - Maintain attention - Sleep-wake cycle **Thalamus Function: Relay Neural Signals From PNS** - Relay station for afferent tracts from the PNS - Thalamus receives neural signals from the PNS - Most afferent neural signals (about sensation & movement) from the PNS go through the thalamus before continuing to the target destination - Thalamus has specialized functions to process sensory data - Cell nuclei process neural signals for all sensory information except smell (pain, temperature, touch, sense of noxiousness) - Thalamus processes these signals before they go to the cortex - Then sends sensory info to the cortex **Lateral Geniculate (Cell) Body (LGB) in Thalamus** - Receives visual sensory information from the retina - Routes to the visual cortex of the occipital lobe **Medial Geniculate (Cell) Body (MGB) in Thalamus** - Receives auditory sensory information from the inferior colliculus (IC) in the auditory pathway -- routes the signals to the primary auditory cortex in the temporal lobe - Important for the direction and maintenance (mediating) of our attention **Anterior Region and Mediodorsal Region in Thalamus** - Areas connect to areas of the CNS that play important roles in - Executive functions, memory - Mood, emotions - Personality - Ability to understand how physical state can impact cognition (e.g., tired during an exam) **Thalamus Disorders Overview** - Most often damaged by stroke - Blood supply to thalamus differs across people - So hard to predict the effects of a vascular lesion in this area - Area can be affected by degenerative diseases - E.g., dementia **Speech** - Thalamus works with the basal ganglia, so it is possible to have speech problems with thalamus damage but not common - Dysarthria - Apraxia of speech **Language** - Thalamic aphasia - Lesions in the thalamus, plus usually other areas of the CNS - Deficits usually mild - Problems with - Comprehension - Anomia and paraphasias - Reduces comprehension of emotional cues (receptive aprosiodia as part of apragmatism) can occur - Severe case: could see mutism **Cognition** - Damage to thalamus can cause cognitive problems - Problems resemble damage to prefrontal cortex - Includes deficits - Executive functions, planning, decision making, attention - Impulsivity, behavior, mood, personality disorder - Vision - Visuospatial perception, visual neglect (visual tracts go through thalamus and then to occipital lobe) - Memory - Left thalamus = verbal (language)