Observations on Frontal Lobe Function

Restlessness – animals with bilateral frontal lobe lesions move about consistently and aimlesslyIndifference – such animals show suppression of curiosity and interestDecreased affect – bifrontal animals show little interest or concern toward other animalsEmotionality – these animals suffer a strong fear of noise, other animals, stimuli which does not disturb them in the natural habitatAbnormal mental state – such animals show defective reflection, judgment, memory, inability to adaptInstincts – certain instincts have been weakenedActivity – tendency toward stereotypic and automatic activities

Observations on Frontal Lobe Function

Restlessness – animals with bilateral frontal lobe lesions move about consistently and aimlesslyIndifference – such animals show suppression of curiosity and interestDecreased affect – bifrontal animals show little interest or concern toward other animalsEmotionality – these animals suffer a strong fear of noise, other animals, stimuli which does not disturb them in the natural habitatAbnormal mental state – such animals show defective reflection, judgment, memory, inability to adaptInstincts – certain instincts have been weakenedActivity – tendency toward stereotypic and automatic activities

Bianchi (1895)

Anatomical Subdivisions of Frontal Cortex

Frontal Subcortical Circuits

Circuits unite functional regions of the frontal cortex with the basal ganglia and thalamus in networks mediating motor activity, eye movements, and behavior. Five circuits have been identified and named according to their function or cortical site of origin.

Frontal Lobes and Executive Dysfunction

About 1/3 of cortex is contained in the frontal lobesArea of the brain that is most “developed” in humans compared to other primatesDamage tends to affect cognitive/behavioral functions typically regarded as uniquely humanDamage to similar areas in different individuals can produce strikingly different impairment

The Frontal Lobes and Executive Dysfunction

Executive functions: Highest order cognitive functionsCapacity for autonomous behavior without external guidanceDirected behavior when goal is remote or absentSelf-direction, self-monitoring, self-regulationAbility to organize a behavioral response to a novel or complex

situation / problemPlanning and regulation of adaptive and goal-directed behaviorProblem solving / reasoning / generating solutions to problemsSpontaneity and fluency of thought and actionCognitive flexibilityStrategic use of memoryAbility to shift cognitive setAbility to inhibit or withhold responses as appropriateAbility to focus or sustain attention (inhibit attentional capture by

nonrelevant stimuli)

Two Broad Frontal Syndromes

1. Dorsolateral prefrontal syndrome Lowered general arrousal Impaired attention/distractable Apathy, depressed mood Perseverative behavior Working memory deficits Diminished spontaneous behavior Difficulty with goal-directed behavior “Stimulus Boundedness”

Two Broad Frontal Syndromes2. Ventromedial prefrontal

syndrome Disinhibition of drives Impulsivity Elevated mood Hyperactive Impaired attention

Executive Dysfunction:

•Working memory deficits•Temporal memory / Source memory•Perseveration•Loss of spontaneous behavior•Apathy•Planning deficits/impaired goal-directed behavior•Disinhibition/impulsive behavior•Impaired attention•Depression•Elevated mood

Executive DysfunctionAssociated with:

Frontal lobe brain damage (TBI, CHI, lesions, etc.)DementiaMajor depressionParkinson’s/Huntington’s diseaseHIV-Related DementiaSubcortical strokesSchizophreniaAlcoholic Dementia (Wernicke-Korsakoff syndrome)

Memory-related deficits

Working memory: delayed response tasksTemporal memory: when did the event occur?Source memory: where did I get this information from?Confabulation: production of fabricated accounts of past events Momentary – plausible but incorrect memories

which fill the gap Fantastic – unnecessary and implausible

memories (e.g., story is a wild concoction of past events)

Inhibition-Related Deficits

PerseverationInability to inhibit a dominant response setSocial Disinhibition/ImpulsivityLoss of spontaneous behaviorPoor planning/goal-directed behavior?Attentional deficits?

Mood/Affect/Emotion Symptoms

DepressionMood elevationApathy/IndifferenceAgitationDisinhibition/Impulsivity“Personality Change”

Phineous Gage

Railroad foremanWell-respected, hard-working1848: tamping iron accidentHe never lost consciousness, and had no obvious neurological symptomsBut he was “no longer Gage”

Phineous Gage

Gage’s Doctor described Gage’s post accident personality as Fitful, irreverent, indulging at times in the greatest profanity which was not previously his custom, manifesting but little deference for his fellows, impatient of restraint and advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operation, which are no sooner arranged than they are abandoned … a child in his intellectual capacity and manifestations, he has the animal passions of a strong man.