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Frontal Lobe Syndromes

Outline. Functional anatomy of the frontal lobesNeurotransmitters in the frontal lobes Deficits resulting from frontal lobe insultTesting prefrontal cortical functionCommon causes of frontal lobe syndromes. Functional Frontal Lobe Anatomy . Largest of all lobesSA: ~1/3 / hemisphere3 major area

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Frontal Lobe Syndromes

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    1. Frontal Lobe Syndromes Katalin Gyömörey, Ph.D., M.D.

    2. Outline Functional anatomy of the frontal lobes Neurotransmitters in the frontal lobes Deficits resulting from frontal lobe insult Testing prefrontal cortical function Common causes of frontal lobe syndromes

    3. Functional Frontal Lobe Anatomy Largest of all lobes SA: ~1/3 / hemisphere 3 major areas in each lobe Dorsolateral aspect Medial aspect Inferior orbital aspect

    4. Functional Frontal Lobe Anatomy

    5. Motor cortex Primary Premotor Supplementary Frontal eye field Broca’s speech area Functional Frontal Lobe Anatomy

    6. Motor Cortex Primary motor cortex Input: thalamus, BG, sensory, premotor Output: motor fibers to brainstem and spinal cord Function: executes design into movement Lesions:?/? tone; ? power; ? fine motor function on contra lateral side

    7. Motor Cortex Premotor cortex Input: thalamus, BG, sensory cortex Output: primary motor cortex Function: stores motor programs; controls coarse postural movements Lesions: moderate weakness in proximal muscles on contralateral side

    8. Motor Cortex Supplementary motor Input: cingulate gyrus, thalamus, sensory & prefrontal cortex Output: premotor, primary motor Function: intentional preparation for movement; procedural memory Lesions: mutism, akinesis; speech returns but it is non-spontaneous

    9. Motor Cortex Frontal eye fields Input: parietal / temporal (what is target); posterior / parietal cortex (where is target) Output: caudate; superior colliculus; paramedian pontine reticular formation Function: executive: selects target and commands movement (saccades) Lesion: eyes deviate ipsilaterally with destructive lesion and contralaterally with irritating lesions

    10. Motor Cortex Broca’s speech area Input: Wernicke’s Output: primary motor cortex Function: speech production (dominant hemisphere); emotional, melodic component of speech (non-dominant) Lesions: motor aphasia; monotone speech

    11. Prefrontal Cortex Orbital prefrontal cortex Connections: temporal,parietal, thalamus, GP, caudate, SN, insula, amygdala Part of limbic system Function: emotional imput, arousal, suppression of distracting signals Lesions: emotional lability, disinhibition, distractibility, ‘hyperkinesis’

    12. Prefrontal Cortex Dorsomedial prefrontal cortex Connections: temporal,parietal, thalamus, caudate, GP, substantia nigra, cingulate Functions: motivation, initiation of activity Lesions: apathy; decreased drive/ awareness/ spontaneous movements; akinetic-abulic syndrome & mutism

    13. Prefrontal Cortex Dorsolateral prefrontal cortex Connections: motor / sensory convergence areas, thalamus, GP, caudate, SN Functions: monitors and adjusts behavior using ‘working memory’ Lesions: executive function deficit; disinterest / emotional reactivity; ? attention to relevant stimuli

    14. Neurotransmitters Dopaminergic tracts Origin: ventral tegmental area in midbrain Projections: prefrontal cortex (mesocortical tract) and to limbic system (mesolimbic tract) Function: reward; motivation; spontaneity; arousal

    15. Neurotransmitters Norepinephrine tracts Origin: locus ceruleus in brainstem and lateral brainstem tegmentum Projections: anterior cortex Functions: alertness, arousal, cognitive processing of somatosensory info

    16. Neurotransmitters Serotonin tracts Origin: raphe nuclei in brainstem Projections: number of forebrain structures Function: minor role in prefrontal cortex; sleep, mood, anxiety, feeding

    38. Frontal Lobe Syndromes – Summary Personality and emotional changes Reflect prefrontal lesions Role of Dopamine and Norepinephrine Trauma > vascular, tumors

    39. Functional Frontal Lobe Anatomy Five ‘frontal subcortical circuits’ (Cummings,‘93) Motor Oculomotor Dorsolateral prefrontal Lateral orbitofrontal Anterior cingulate

    40. ‘Frontal subcortical circuits’ Functional Frontal Lobe Anatomy

    41. Frontal subcortical Circuits: 1. Motor Circuit Supplementary Motor & Premotor: planning, initiation & storage of motor programs; fine-tuning of movements Motor:final station for execution of the the movement according to the design

    42. Frontal subcortical Circuits: 2. Oculomotor Circuit Voluntary scanning eye movement Independent of visual stimuli

    43. Frontal subcortical Circuits: 3. Dorsolateral Prefrontal Circuit Executive functions: motor planning, deciding which stimuli to attend to, shifting cognitive sets Attention span and working memory

    44. Frontal subcortical Circuits: 4. Lateral Orbitofrontal Circuit Emotional life and personality structure Arousal, motivation, affect Orbitofrontal cortex: consciousness

    45. Frontal subcortical Circuits: 5. Anterior Cingulate Circuit Abulia, akinetic mutism

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