Frontal lobes

Frontal lobes

Anatomy of the frontal lobes
1. Constitute 20% of the neocortex
2. Subdivisions
  1. Motor
    1. Area 4
  2. Premotor
    1. Areas 6, 8
  3. Premotor cortex
    1. Lateral area 6
  4. Supplementary motor cortex
    1. Medial area 6
  5. Frontal eye field
    1. Area 8
  6. Supplementary eye field
    1. Area 8A
  7. Prefrontal cortex
    1. Area of frontal lobe that receives input from the dorsomedial nucleus of the thalamus
    2. Divisions
      1. Dorsolateral prefrontal cortex
      2. Inferior frontal cortex
      3. Medial frontal cortex
Connections of the motor and premotor areas
1. Motor cortex
  1. Projects to spinal motor neurons, cranial nerves that control the face
  2. Projects to the basal ganglia and the red nucleus
2. Premotor
  1. Projections to the motor cortex
  2. Projections to the spinal cord
  3. Receives projections from parietal areas PE and PF
  4. Receives projections from dorsolateral prefrontal area
3. Eye fields
  1. Receive from PG and the superior colliculus
Connections of the prefrontal areas
1. End of dorsal and ventral streams of visual input
2. Dorsolateral prefrontal area
  1. Reciprocal connections with the posterior parietal and STS
  2. Extensive connections with the cingulate cortex, basal ganglia and superior colliculus
  3. Receives input from dopaminergic cells in tegmentum
3. Orbital frontal cortex
  1. Receives from the temporal lobe, amygdala, gustatory cortex, somatosensory cortex, olfactory cortex, dopaminergic cells in tegmentum
  2. Projects to hypothalamus and amygdala
Frontal lobe function
1. Planning and selection
2. Persistence and ignoring distracting stimuli
3. Memory for what you have already done
4. Executive functions
5. Responds to both internal, external and context cues
Functions of the premotor cortex
1. Selects movements to be executed
2. Functions to choose behaviour in response to external cues
3. An increase in activity in the premotor cortex is seen when cues become associated with movement
Functions of the prefrontal cortex
1. Controls cognitive processes so that appropriate movements are selected at the correct time
2. Internal cues
  1. Temporal memory
    1. Memory for what has just happened
3. External cues
  1. Feedback about rewarding properties of stimuli
  2. Orbital frontal cortex
    1. Learning by association
4. Context cues
  1. Orbital ftontal
    1. Social interactions
5. Autonoetic awareness
  1. Self knowledge
Asymmetry of the frontal lobes
1. Left
  1. Language
  2. Encoding memories
2. Right
  1. Retrieving memories
  2. Non verbal movements, facial expression
Symptoms of frontal lobe lesions
1. Disturbances of motor function
  1. Loss of fine movements, speed and strength
    1. Appears after damage to the primary motor cortex
  2. Loss of movements programming
    1. Damage to the premotor or dorsolateral cortex
  3. Changes in voluntary gaze
    1. Damage to the frontal eye fields
  4. Speech problems
    1. Damage to Broca's area
      1. Agrammatism
    2. Damage to the supplementary motor cortex
      1. Mute
2. Convergent vs. divergent thinking
  1. Convergent thinking
    1. Only one answer to the question
  2. Divergent thinking
    1. Questions that ask for a variety of responses
  3. Frontal lobe patients are impaired on divergent thinking
3. Loss of behavioural spontaneity
  1. Decreased verbal fluency
  2. Decreased design fluency
  3. Reduction in general behaviour
4. Increased perseveration
5. Inability to form a strategy
  1. Larger deficit when completing novel tasks
6. Loss of response inhibition
  1. The Stroop test
  2. The Wisconsin card sorting task
7. Deficits in self regulation
8. Take more risks
  1. Iowa gambling task
    1. Appears after damage to the orbitofrontal cortex
9. Loss of associative learning
  1. Inability to select from competing responses
10. Impaired social and sexual behaviour
  1. Phineas Gage
  2. Changes in personality
    1. Pseudodepression
      1. Lesions of left frontal lobe
      2. Outward apathy, indifference, loss of initiative
      3. Reduced sexual interest, little or no verbal output
    2. Pseudopsychopathy
      1. Lesions of the right frontal lobe
      2. Immature behaviour, lack of tact and restraint
      3. Promiscuous sexual behaviour
      4. Coarse language, lack of social graces, increased motor activity
  3. Deficits in social and sexual behaviour
    1. Orbitofrontal lesions
      1. Reduces inhibitions with abnormal sexual behaviour
      2. Leads to deficits in identifying facial expressions
    2. Dorsolateral lesions
      1. Reduce interest in sexual behaviour
11. Spatial deficits
  1. May be a role for the frontal lobe in selective visual locations
12. Symptoms associated with damage to the frontal facial area
  1. Sensory and motor functions of the face are preserved after damage
  2. Left - loss of verbal fluency
  3. Right - loss of design fluency
Diseases affecting the frontal lobe
1. Schizophrenia
  1. Abnormality in the mesocortical dopaminergic projection
  2. Decrease in blood flow to the frontal lobes and frontal lobe atrophy
2. Parkinson's disease
  1. Loss of dopamine cells in the substantia nigra that project to the prefrontal cortex
3. Korsakoff's
  1. Alcohol induced damage to the dorsomedial thalamus and a deficiency in the frontal lobe catecholamines

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	Created by andreaarose over 10 years ago