Localizaiton of tests within frontal lobes

Stuss DT. Levine B.  Adult clinical neuropsychology: lessons from studies of frontal lobes.  Ann Rev Psychol 2002; 53: 401-433.

Long article, a few (random) points distilled out, heavily tilted towards localization of neuropsych tests within frontal lobes.

Anatomically, the ventral prefrontal cortex is dissociated from the dorsolateral prefrontal cortex (DLPFC).  The former, is associated with emotional regulation, evolutionarily emerged from orbitofrontal and olfactory cortex and limbic nuclei.  It also is important for inhibition, emotion and reward processing.  By contrast, the DLPFC evolutionarily comes from archicortical trend of hippocampus, and is involved in spatial and conceptual processing, including executive functioning.  The frontal poles are more recently evolved and are involved in self awareness, autonoetic consciousness, and humor.

By function:

Frontal lobe language (key reference is Alexander MP et al., 1989 Brain Lang. )  excluding articulation and Broca's aphasia, frontal language function and dysfunction is grouped under activation and formulation (paralinguistics).  Dynamic aphasia, or trouble activating language, occurs after damage to SMA or ACC. TMA, with truncated language, occurs after damage to left DLPFC.  (in other publications, Alexander refers to 'subbcallosal fasciculus').   Usually this is tested using letter fluency.  In Stuss 1998 (JINS) rview of 74 local lesion patients, left DLPFC patients were most impaired, right DLPFC and VPFC patients were not impaired.  However left parietal lesioned patients also were impaired and could not be differentiated from left DLPFC patients.  Superior medial damage on either side (SMA) was associated with poor productions, and posterior superior lateral temporal lesions were implicated .  The latter could be teased out  by switching between letter and semantic fluency tasks.  All above are left sided lesions (except SMA).  Discourse lesions that are left sided include simplification, perseveration and omissions. Right sided lesions may cause amplification of details, wandering from topic, insertion of irrelevancies, and dysprosody, leading to incoherence.

Control of Memory:

Its important to differentiate between basic associative cue-engram processes (medial temporal lobe/hippocampal structures) and strategic processes that may be more top down such as coordination, elaboration and interpretation of these processes.  Wechsler Memory Scale and many others tap both processes but make no effort to dissociate them.  Author cites CVLT as an example of the "Boston approach" that includes efforts to measure serial position learning, semantic organization, interference effects, cued recall, recognition and response bias. Most recent WMS revision has semantically unrelated words, precenting analysis of semantic clustering.  Stuss et al. 1994 Psychology showed right DLPFC lesion patients had more intralist repetitions due to response monitoring defect.  Left frontal caused problems with encoding, retrieval and recognition.  Frontal lobes are important to retrieval involving monitoring, verification, & placement of information especially in spatial and temporal contexts, with lesions causing reduplication, confabulation and retrograde amnesia.  There is a right hemispheric bias in retrieval, but also a DLPFC/VPFC wherein latter is involved in retrieval cue specification and former in higher level postretrieval monitoring (see Fletcher, 1998 Brain, also Petrides). 

Working Memory:
Original idea jacobsen 1936 monkeys with frontal lesions could not make decisions once stimulus was removed from view.  Frontal lobe involvement keeps information online while other areas (slave systems) perform operations.  Frontal involvement increases with interference .  DLPFC monitors and manipulates, whereas VPFC maintains, controls interference and inhibition.  Digit span/spatial span give information about working memory storage capacity but not rehearsal or executive control.  Frontal lesions in one study did not affect digit span.  Reverse digit span measures manipulation of above.  Brown-Peterson technique taps interference.  Supraspan tests measure processing when capacity is exceeded.  Not standard.

Anterior attention processes
Attentional switching:  WCST and TMT, part B.  WCST originally shown by Milner to be response to frontal damage.  New problem solving Dias et al. (J Neurosci 1997).  .  WCST shifts are extradimensional eg. color to form, on basis of feedback, or intradimensional, eg within a color red to blue.  Extradimensional shifts are due to DLPFC in healthy adults.  VPFC damage does not affect extradimensional shifting.  However, VPFC lesions could contribute to the relatively rare error of loss of set due to susceptibility to interference.  DLPFC patients also had loss of set due to loss of sustained attention.Posterior damage also can affect WCST. 

TMT Part B ostensibly uses Part A as an internal control for factors other than switching, but has been criticized as not well matched to Part B in other respects.  Stuss et al. found time correlated with frontal pathology, but effect was eliminated when score was corrected for TMT Part A.  DLPFC patients were distinguished from Part A based on errors but not time.

Selective attention: Stroop test
Stuss found deficit in left sided lesions was due to problems in color naming, not interference.  (Stuss et al., Neuropsychologia 2001).  Patients with superior medial lesions showed errors due to importance of area in maintaining an activated intention.  Inferior medial patients were normal.

Sustained attention:
Continuous performance tests are sensitive to frontal damage especially with increased complexity (eg. respond to "O" after "x".  The Sustained Attention to Response Tast (SART, Robertson 1997 Neuropsychologia) and the Elevator Counting Test (Robertson 1991  the Test of Everyday Attention)

VPFC important in acquiring and reversing stimulus/reward.  The Iowa Gambling Test (Bechara et al.) is based on Somatic Marker Hypothesis, that reasoning is constrained based on previous conditioning, mediated by ventromedial frontal lobes.  VPFC lesions cause "self regulatory disorder" or "SRD."  Another test is the Strategy Application Test, based on the Six Element Test of Shallice and Burgess.  Every patient with focal VPFC damage, especially on right was impaired.  It correlated with outcome questionnaires.

Frontal Pole:  Autobiographical Memory Test.  (Kopelman, 1989J Clin Exper Neuropsychol).  Also, Dysexecutive Questionnaire (Burgess et al, 1996