Brain-Behavior Relationships
PREFRONTAL CORTEX
Overview of Topics
Prefrontal Cortex
Responsible for planning, structuring, and evaluating voluntary (goal directed behavior, i.e., activities requiring the constant comparison of planned acts with the effects achieved.
A. Deficits associated with lesions of the prefrontal cortex
- With minor lesions
- Inability to prevent rapid extinction of orienting response following verbal instruction (1).
- Disturbances in regulatory role of speech (1).
- Disturbances in complicated gnostic functions (e.g. understanding complicated pictures, thematic pictures, comprehension of written text) (1).
- Problem solving difficulties associated with disturbances in selective organization of mental activity (i.e. serial sevens) (1, 3).
- Deficits in complex tasks requiring inhibition of habitual behavior patterns (2, 8, 10).
- Difficulties with actions requiring a series of movements, less severe when accompanied by external verbalization (Fist, edge, palm) (1, 5).
- Difficulties in task executions when instructions or prompts conflict with what would be expected, although ability to carry out simple instructions is unimpaired (visual or verbal) (3).
- Difficulties tapping at successive groups of rhythms or drawing a series of figures that alternate in pattern (1, 3) (tendency to perseverate).
- Decreased spontaneity, decreased rate of behavior, decreased range of interests, loss of initiative, and impulsiveness without self-corrective action may be early signs (1, 4).
- Deficits in visual tracking and scanning, especially on complex tasks (6).
- Difficulty in constructing mirror-image relationships, especially if complex (3).
- With more extensive lesions.
- Perseveration: difficulties in making behavioral shifts in attention, movement, and attitude (6, 14).
- Concreteness(7) & decreased creativity(6).
- Inflexibility in cognitive, perceptual and motor modalities (6).
- Poor recall of thematic verbal material (paragraphs) (1).
- Poor recall of verbal & nonverbal series, with contamination of first & subsequent series (1).
- Deficits in comprehension of logical-grammatical (prepositional) constructions (e.g. "place a cross beneath the circle.") (3).
- Difficulties in writing associated with fatigue, progressively smaller characters, perseveration, loss of overall plan (i.e. letter transpositions, etc.) (3).
- Deficits in abstract/categorical intellect(2).
- Take longer to learn go-no go tasks and make more false positive responses (9,3, particularly with medial frontal lesions (15).
- Diminished visual scanning and tracking, resulting in impulsive judgments which are based on the perception of a single aspect of a stimulus(2,6,11).
- Performance of relatively simple task is impaired by perseveration; however, overlearned tasks are conducted without difficulty (2).
- Increased level of distractibility, especially to small noises or events (12).
- Memory curve plateaus early (approximately 5 items), even with rehearsal (2, 12).
- Disturbances in selective memory with confabulation (2, 12).
- Defects in time sense with respect to recency and time span Judgments (6, 24) and disturbances of temporal orientation (13, 25) occurring with bilateral frontal lobe lesions.
- More superior lesions produce motor disturbances, while inferior lesions produce speech disturbances (2)
- Increased trend toward confabulation (2,12).
- Magnitude of deficit is associated with the cause of the lesion (i.e. surgery or degenerative) (5) and the presence of generalized physical disorders (i.e. hypertension) (2). Also, deficits are more severe with bilateral involvement (5).
- Constructive intellectual activity may be distributed when preliminary analysis and formation of a plan is required (not constructional apraxia per se) (2).
- Diminished critical self-evaluation of behaviors; no distress or attempts at correction (2,12).
- Able to perform firmly-established verbal analogies (father: son: Mother, but difficulty in forming unfamiliar analogies (2)
- Poor capacity for arithmetic tasks involving a series of analytic steps, although often able to solve simple problems. Tend to make impulsive judgments (2).
- Emotional disturbances seen as two principle reactions: inhibition (apathy, narrowing of interests, flattered affect, withdrawal) and disinhibition (euphoria, impulsivity, irritability, anxiety, obscene language (2, 6, 16, 18).
- Symptoms of frontal lobe lesions with increased intracranial pressure can include headache and somnolence (16).
- With medial orbital lesions
- More often associated with emotional changes such as apathy or hyperactivity (11).
- Defects in sorting or abstraction tasks usually not observed (17); gross intellectual changes also not apparent (2).
- Olfactory & visual disturbances may occur 12).
- Emotional alterations can range from apathy to short-term lability (4).
- Lateral dorsal lesions
- Associated more with intellectual deficits (4).
- Perseveration is more common: associated with impaired shifting in attention and thinking (4).
- With extensive lesions, gross perseveration may occur even though patient recognizes as inappropriate (4).
- Impaired categorical thinking apparent (4).
- Left hemisphere prefrontal lesions
- Deficits in tests of categorization and flexibility (5).
- Problems with body schema (autopagnosia) due to problems of scanning, perceptual shifting and postural mechanisms (19).
- Marked inactivity affects general intellectual processes and behavior (2).
- Cannot change verbal instructions into acts, especially when the instructions are complex or symbolic (20).
- Decreased spontaneity of speech; may result in complete loss of voluntary speech (12).
- Memory deficits for verbal material (2); however, deficits may be due to defective registration (21).
- Right hemis. prefrontal lesions
- Constructional apraxia, associated with motor rather than perceptual difficulties (6); deficits may occur as a function of impaired complex (3-D) spatial analysis (13).
- Large lesions may exist without obvious symptoms; serious speech disorders usually not seen in right hemisphere lesions (5).
- Difficulty with drawing tasks (13), though this is associated more with right hemisphere lesions in general (6).
- Impaired visual-spatial integration (22), maze learning (23), non-verbal visual memory (10).
- With very severe lesions there may be a complete disintegration of behavior as observed in many of the following: nonreactive to environmental cues or instructions from self to others, reactive to irrelevant stimuli, echolalia, mutism (loss of voluntary speech), agraphia, confusion, and generalized slowing (6, 12).
* Even though, following the Luria approach (12), we have chosen to distinguish lesser from more extensive lesions, this distinction is somewhat arbitrary. Research suggests that the distinction is based on quantitative rather than qualitative differences. That is, with lesser lesions, one could expect to find deficits similar to those seen in cases of more extensive lesions; however, such deficits would obviously he of less magnitude. Likewise, the types of deficits associated with less extensive lesions would undoubtedly be observed in more extensive cases.
B. Tests - Prefrontal Lobe Function
- Wisconsin Card Sort: left > right (5,26,27)
- Word fluency: L > R (5,13,24)
- Halstead Categories Test: L > R (5)
- Trail Making, Part B: L > R (4, 5)
- Color and word page of Stroop Color and Word Test: L > R (5,8)
- Temporal orientation test: bilateral (13)
- Verbal associative learning: bilateral (13, 28)
- Personal identification test(body schema): L>R(6)
- Picture Arrangement: R > L (28)
- Memory for Designs: R > L (28)
- 3-D Constructional praxis test: R > L (13)
- Object classification test: Right frontal and left parietal (29).
- Link's cubes (building a large cube from differently colored small cubes): R > L 12)
- Reaction of choice tests (two choices), such as go-no go: L > R on more complex tasks (2, 9).
- Impairment on tests requiring complex picture and Raven's Progressive Matrices) (3)
- Depressed digit span: L > R (28).
References
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