15.3. The Right Frontal Lobe
The distributed functions of the right frontal lobe are most involved with emotional control and inhibitory control over the limbic system. Deficits in this lobe are associated with disinhibition of personal behavior, hygiene and sexual conduct. Patients demonstrate "witzelsucht" (inappropriate jocularity) and impersistence.
- Disinhibition:
- Personal behavioral
- Hygiene
- Sexual activity
- Inappropriate jocularity "witzelsucht"
- Impersistence of a motor task
- Neglect and directional hypokinesis of left hemispace
- Stimulus familiarity and novelty abnormalities
- False recognition syndrome with confabulation
Minor Right Frontal Lobe Deficits
- Understanding and mediating negative emotions
- BA 6 and BA 8 lesions are associated with simultanapraxia (inability to coordinate both sides of the body to accomplish a motor function)
- Right frontal eye fields direct bilateral search of the visual landscape
- Retrieving the temporal order of stimuli
Dorsolateral Prefrontal Cortex
The dorsolateral prefrontal cortex (DLPC) is important as a store of knowledge to solve problems of the immediate environment, to perform internally generated motor tasks and to perform complex behavioral motor functions requiring multiple sequences. It is important in memory retrieval that is pivotal for working memory. The frontal eye fields are located in the DLPC which initiate saccadic eye movements and are important in ocular fixation.
Prefrontal cortex dysfunction may present as a pseudodepressed syndrome manifesting psychomotor inhibition, apathy, indifference, lack of drive and decreased emotional reactivity.
DLPC (Major Behavioral Deficits)
- Pseudodepression syndrome
- Psychomotor inhibition
- Apathy
- Indifference
- Lack of drive
- Decreased emotional reactivity
Other Behavioral Deficits of DLPC
- Obsessive-compulsive behavior
- Ventromedial prefrontal:
- Aggressive violent behavior
General Deficits of DLPC
- Decreased procedural learning
- Decreased ability to index events in time
- Failure to develop internal references
- Parapraxia
- Working memory
- Deficits of awareness of near extrapersonal space
- Space that is within the grasp of the examiner
- Switching motor programs
- Abulia-telephone (response)
- Post stroke depression:
- Severity of depression is related to the proximity of the lesion to the frontal pole
- Release of approach behavior
SMA (Supplementary Motor Cortex)
The supplementary motor cortex is instrumental in coordinating the muscle activation of both sides of the body, speech, and the generation, temporal sequence and preparation of movements.
- Aphasia (similar to Broca's)
- Motor function:
- Coordinating movements of both sides of the body during a task (walking; swing phase and stance phase)
- Generation of movement (important for designing engrams of movement)
- Temporal sequence of a motor task
- Entraining motor sequences
- Mirror movements (may be seen if damaged)
- Response to internal cues
- Priming (encoding of consciously inaccessible knowledge)
- Sequentially memory guided saccades
Orbitofrontal Cortex
- Pseduo-psychopathic behavior:
- Disinhibition
- Facetiousness
- Sexual/personal behavior
- Lack of concern for the effects of behavior
- Bilateral lesions cause retrograde amnesia
- Failure to break previously learned associations
- Medial orbital frontal lesions are associated with confabulation
- Mania
- Autonomic regulation of vagal tone
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