The Frontal Lobes Readings: KW Ch. 16 Portrait: Losing Frontal-Lobe Functions E.L. Highly organized college professor Became disorganized, showed little emotion, and began to miss deadlines Scores on intelligence and memory tests were superior Showed impairment on frontal lobe tests Anatomy of the Frontal Lobes Constitute 20% of the neocortex Subdivisions Motor: Area 4 Premotor: Areas 6 and 8 Can be divided into: Lateral area 6: Premotor cortex Medial area 6: Supplementary motor cortex Area 8: Frontal eye field Area 8A: Supplementary eye field Anatomy of the Frontal Lobes Prefrontal Cortex Area of the frontal lobe that receives input from the dorsomedial nucleus of the thalamus Divisions Dorsolateral Prefrontal Cortex Inferior Frontal Cortex Also called Orbitofrontal cortex Medial Frontal Cortex Sometimes considered part of the cingulate Many areas of the frontal lobe are multimodal 1
Connections of the Motor and Premotor Areas Motor Cortex Projects to spinal motor neurons, cranial nerves that control the face Projects to the basal ganglia and the red nucleus Premotor Projections to the spinal cord Projections to the motor cortex Connections of the Motor and Premotor Areas Premotor Receives projections from parietal areas PE and PF Receives projections from dorsolateral prefrontal area Eye fields Receive from PG and the superior colliculus Connections of the Prefrontal Areas End of dorsal and ventral streams of visual input Dorsolateral Prefrontal Area Reciprocal connections with the posterior parietal and STS Extensive connections with the cingulate cortex, basal ganglia, and superior colliculus Receives input from dopaminergic cells in tegmentum Connections of the Prefrontal Areas Orbital Frontal Cortex Receives from the temporal lobe, amygdala, gustatory cortex, somatosensory cortex, olfactory cortex, dopaminergic cells in tegmentum Projects to hypothalamus and amygdala 2
A Theory of Frontal-Lobe Function Planning and selection Persistence and ignoring distracting stimuli Memory for what you have already done Executive Functions Responds to both internal, external, and context cues Functions of the Premotor Cortex Selects movements to be executed Functions to choose behavior in response to external cues An increase in activity in the premotor cortex is seen when cues become associated with movement Functions of the Prefrontal Cortex Controls cognitive processes so that appropriate movements are selected at the correct time Internal Cues Temporal memory: Memory for what has just happened External Cues Feedback about rewarding properties of stimuli Orbital Frontal Cortex - Learning by association Functions of the Prefrontal Cortex Context Cues Orbital Frontal - Social Interactions Autonoetic Awareness Self knowledge Binding together the awareness of oneself as continuous through time Asymmetry of the Frontal Lobes Left Language Encoding memories Right Nonverbal movements, facial expression Retrieving memories 3
Heterogeneity of Frontal-Lobe Function Frontal lobes perform a variety of functions Frontal damage is unlikely to produce impairment to all functions Snapshot: Heterogeneity of Function in the Orbitofrontal Cortex Stephen Frey and Michael Petrides Examined functions of the orbital region using PET Increased activity in area 13 to unpleasant auditory stimuli Increased activity in area 11 when learning new visual information Functional dissociation between the two areas Area 13: Responds to affective qualities Area 11: Processes new visual information Disturbances of Motor Function Loss of fine movements, speed, and strength Typically appears after damage to the primary motor cortex Loss of movement programming Damage to the premotor or dorsolateral cortex Changes in voluntary gaze Damage to the frontal eye fields 4
Disturbances of Motor Function Corollary discharge or reafference Internal neural signal that movement will occur Frontal lobe damage disrupts corollary discharge Speech Problems Damage to Broca s area Agrammatism Damage to the supplementary motor cortex Mute Convergent vs. Divergent Thinking Convergent thinking: Only one answer to the question Divergent thinking: Questions that ask for a variety of responses Frontal lobe patients are impaired on divergent thinking Loss of behavioral spontaneity Decreased verbal fluency Decreased design fluency Reduction in general behaviors The Wisconsin Card Sorting Test Increased perseveration Inability to form a strategy Larger deficit when completing novel tasks Loss of response inhibition The Wisconsin Card Sorting Task The Stroop Test 5
The Stroop Test Take more risks Iowa Gambling Task Appears after damage to the orbitofrontal cortex Deficits in self-regulation Loss of associative learning Inability to select from competing responses Testing Associative Learning Poor Temporal Memory Five animal experiments indicate a role for the frontal lobe in temporal memory Area 46 Role in providing an internal representation of spatial information Active during delayed response test Medial regions Role in object recognition Experiments Showing Deficits of Temporal Memory Poor Temporal Memory Studying Temporal Memory in Humans Recency memory Tests memory for the order in which things have occurred Frontal lobe patients show impairment on this task Recent Findings on Temporal Memory Critical role for the prefrontal cortex Fuster and colleagues Single cell recording of sensory associations across time 6
Impaired social and sexual behavior Example: Phineas Gage Impaired social and sexual behavior Changes in personality Pseudodepression Appears after lesions of the left frontal lobe Outward apathy, indifference, loss of initiative Reduced sexual interest, Little or no verbal output Pseudopsychopathy Appears after lesions of the right frontal lobe Immature behavior, lack of tact and restraint Promiscuous sexual behavior Coarse language, lack of social graces, increased motor activity Impaired social and sexual behavior Deficits in Social and sexual behavior Orbitofrontal lesions Reduce inhibitions and may introduce abnormal sexual behavior Leads to deficits in identifying facial expressions Dorsolateral lesions Reduce interest in sexual behavior Spatial Deficits? May be a role for the frontal lobe in selecting visual locations Symptoms Associated with Damage to the Frontal Facial Area Sensory and motor functions of the face are preserved after damage Left: Loss of verbal fluency Right: Loss of design fluency Clinical Neuropsychological Assessment of Frontal Lobe Damage 7
Imaging Frontal Lobe Function Diseases Affecting the Frontal Lobe Schizophrenia Abnormality in the mesocortical dopaminergic projection Decrease in blood flow to the frontal lobes, and frontal lobe atrophy Parkinson s Disease Loss of dopamine cells in the substantia nigra that project to the prefrontal cortex Korsakoff s Alcohol-induced damage to the dorsomedial thalamus and a deficiency in frontal lobe catecholamines 8