Frontal lobes

Frontal lobes

1. Anatomy of the frontal lobes

   • Constitute 20% of the neocortex
   • Subdivisions
     • Motor
       • Area 4
     • Premotor
       • Areas 6, 8
     • Premotor cortex
       • Lateral area 6
     • Supplementary motor cortex
       • Medial area 6
     • Frontal eye field
       • Area 8
     • Supplementary eye field
       • Area 8A
     • Prefrontal cortex
       • Area of frontal lobe that receives input from the dorsomedial nucleus of the thalamus
       • Divisions
         • Dorsolateral prefrontal cortex
         • Inferior frontal cortex
         • Medial frontal cortex

2. 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 motor cortex
     • Projections to the spinal cord
     • Receives projections from parietal areas PE and PF
     • Receives projections from dorsolateral prefrontal area
   • Eye fields
     • Receive from PG and the superior colliculus

3. 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
   • Orbital frontal cortex
     • Receives from the temporal lobe, amygdala, gustatory cortex, somatosensory cortex, olfactory cortex, dopaminergic cells in tegmentum
     • Projects to hypothalamus and amygdala

4. 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

5. Functions of the premotor cortex

   • Selects movements to be executed
   • Functions to choose behaviour in response to external cues
   • An increase in activity in the premotor cortex is seen when cues become associated with movement

6. 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
   • Context cues
     • Orbital ftontal
       • Social interactions
   • Autonoetic awareness
     • Self knowledge

7. Asymmetry of the frontal lobes

   • Left
     • Language
     • Encoding memories
   • Right
     • Retrieving memories
     • Non verbal movements, facial expression

8. Symptoms of frontal lobe lesions

   • Disturbances of motor function
     • Loss of fine movements, speed and strength
       • Appears after damage to the primary motor cortex
     • Loss of movements programming
       • Damage to the premotor or dorsolateral cortex
     • Changes in voluntary gaze
       • Damage to the frontal eye fields
     • 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 behavioural spontaneity
     • Decreased verbal fluency
     • Decreased design fluency
     • Reduction in general behaviour
   • Increased perseveration
   • Inability to form a strategy
     • Larger deficit when completing novel tasks
   • Loss of response inhibition
     • The Stroop test
     • The Wisconsin card sorting task
   • Deficits in self regulation
   • Take more risks
     • Iowa gambling task
       • Appears after damage to the orbitofrontal cortex
   • Loss of associative learning
     • Inability to select from competing responses
   • Impaired social and sexual behaviour
     • Phineas Gage
     • Changes in personality
       • Pseudodepression
         • Lesions of left frontal lobe
         • Outward apathy, indifference, loss of initiative
         • Reduced sexual interest, little or no verbal output
       • Pseudopsychopathy
         • Lesions of the right frontal lobe
         • Immature behaviour, lack of tact and restraint
         • Promiscuous sexual behaviour
         • Coarse language, lack of social graces, increased motor activity
     • Deficits in social and sexual behaviour
       • Orbitofrontal lesions
         • Reduces inhibitions with abnormal sexual behaviour
         • Leads to deficits in identifying facial expressions
       • Dorsolateral lesions
         • Reduce interest in sexual behaviour
   • Spatial deficits
     • May be a role for the frontal lobe in selective 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

9. 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 the frontal lobe catecholamines