Transcript Lec4Figs
Psychology 393 Cognitive Neurology Motor Systems & Apraxia January 30, 2007 Subcortical Motor Control • Two primary structures: – Cerebellum – Basal Ganglia Subcortical Structures: Cerebellum 3 Divisions: • Vermis • Intermediate zone • Lateral zone 3 Nuclei: • Fastigial nucleus • Interpositus nucleus • Dentate nucleus Subcortical Structures: Basal Ganglia • Striatum – Putamen * – Caudate * – Nucleus Accumbens (* Major input zones into Basal Ganglia) • Globus Pallidus – Internal section – External section (Output from BG to Thalamus) • Substantia Nigra • Subthalamic Nucleus Subcortical Structures: Basal Ganglia Important for … • the accomplishment of movements that may take some time to initiate or stop • Two major modulatory roles: – Facilitating/sustaining ongoing action – Suppressing unwanted action Subcortical Structures: Basal Ganglia • Caudate/Putamen (BG input) connects to Globus Pallidus (BG output) by two routes: – Direct Pathway • Activation of Caudate/Putamen inhibits internal GP (iGP). • iGP’s normal inhibition of thalamus (motor nuclei) is inhibited = excitation of thalamic motor nuclei • Excitation of thalamic motor nuclei = facilitation / maintenance of ongoing behaviour Subcortical Structures: Basal Ganglia • Caudate/Putamen (BG input) connects to Globus Pallidus (BG output) by two routes: – Indirect Pathway • Activation of Caudate/Putamen inhibits external GP (eGP). • eGP’s normal inhibition of subthalamic nucleus (STN) is inhibited = excitation of STN • STN in turn excites the inhibitory connections of iGP to thalamus. • Inhibition of thalamic motor nuclei = stopping of unwanted behaviour. Subcortical Structures: Basal Ganglia Damage to Direct Pathway (hypokinetic disorders) • Parkinson’s Disease – Lack of dopaminergic inputs from substantia nigra to striatum • Akinesia (inability to initiate movement) • Bradykinesia (motor slowing) • Resting tremors • Postural disturbances – Once action is begun, difficult to stop – Responses to external stimuli preserved (internally guided / motivated movements disturbed) Subcortical Structures: Basal Ganglia Damage to Indirect Pathway (hyperkinetic disorders) • Huntington’s Disease – Damage to striatum giving rise to indirect pathway • Choreaform movements (uncontrollable jerking / twitching movements) • Athetosis (writhing movements) – Unlike PD (inability to respond to internal stimuli), HD patients may be unable to suppress reactions to somatosensory / kinesthetic stimuli Cortical Motor Control • Involved in externally guided movements – those requiring linkage between sensory inputs and motor outputs • Key Structures – – – – – Primary motor cortex Supplementary motor area Premotor cortex Anterior Cingulate Parietal lobes Cortical Structures: Primary Motor Cortex • Provides command signal to drive motor neurons to make muscles move. • Damage … – weakness – Imprecise fine motor movements Cortical Structures: Premotor Cortex (PMC) / Supplementary motor area (SMA) • Premotor and SMA are involved motor programs – abstract representations of an intended movement (a motor plan) – SMA involved in complicated motor action sequencing – PMC involved in motor action selection (coding for type of action necessary) Cortical Structures: Anterior Cingulate Cortex (ACC) • ACC implicated in motor planning of novel or cognitively demanding actions: – – “A” “B” (well rehearsed) “A” “M” (novel) anterior cingulate activation • Topography for different motor functions – – – Manual – posterior regions Speech – middle regions Ocular – anterior regions Cortical Structures: Parietal Cortex • Twofold role: Superior Parietal Lobule – Integration between motor and sensory information – Damage = difficulty guiding limbs (overreaching) Inferior Parietal Lobule – Contributes to the ability to produce complex, well-learned acts – Damage = difficulty with welllearned motor acts (apraxia) *** Need to know: Table 5.2 Cortical Motor Dysfunction: Apraxia Oral vs. Limb Apraxia • Oral apraxia: – associated with difficulties performing voluntary movements with the muscles of the tongue, lips, cheek, larynx Cortical Motor Dysfunction: Apraxia Oral vs. Limb Apraxia • Limb apraxia: – disrupts the ability to use limbs to manipulate items such as screwdrivers, scissors or hammers. – “Hand as object” errors