Abstract
Design (DF) and phonemic fluency tests (FAS; D-KEFS, 2001) are commonly used to investigate voluntary generation. Despite this, several important issues remain poorly investigated. In a sizeable sample of patients with focal left or right frontal lesion we established that voluntary generation performance cannot be accounted for by fluid intelligence. For DF we found patients performed significantly worse than healthy controls (HC) only on the switch condition. However, no significant difference between left and right frontal patients was found. In contrast, left frontal patients were significantly impaired when compared with HC and right frontal patients on FAS. These lateralization findings were complemented, for the first time, by three neuroimaging; investigations. A traditional frontal subgrouping method found significant differences on FAS between patients with or without Left Inferior Frontal Gyrus lesions involving BA 44 and/or 45. Parcel Based Lesion Symptom Mapping (PLSM) found lower scores on FAS were significantly associated with damage to posterior Left Middle Frontal Gyrus. An increase in rule break errors, so far only anecdotally reported, was associated with damage to the left dorsal anterior cingulate and left body of the corpus callosum, supporting the idea that conflict resolution and monitoring impairments may play a role. Tractwise statistical analysis (TSA) revealed that patients with disconnection; in the left anterior thalamic projections, frontal aslant tract, frontal; orbitopolar tract, pons, superior longitudinal fasciculus I and II performed significantly worse than patients without disconnection in these tracts on FAS. In contrast, PLSM and TSA analyses did not reveal any significant relationship between lesion location and performance on the DF switch condition. Overall, these findings suggest DF may have limited utility as a tool in detecting lateralized frontal executive dysfunction, whereas FAS and rule break behavior appears to be linked to a set of well localized left frontal grey matter regions and white matter tracts.
Highlights
Since the original study of Milner (1964), fluency tasks are amongst the most widely used clinical neuropsychological tests for the detection of frontal lobe dysfunction
We found greater phonemic fluency impairment in patients with Left Inferior Frontal Gyrus (LIFG) lesions involving BA44/45 compared to frontal patients without LIFG lesions in these two areas (Robinson et al, 2012)
Frontal patients and healthy controls (HC) were well-matched for age (t (75) 1⁄4 1.115, p 1⁄4 0.269), gender (χ2 (n 1⁄4 77, df 1⁄4 1) 1⁄4 2.739, p 1⁄4 0.082), years of education (t(56) 1⁄4 -0.697, p 1⁄4 0.489) and National Adult Reading Test (NART) Intelligence Quotient (IQ) (t(68) 1⁄4 -0.065, p 1⁄4 0.949)
Summary
Since the original study of Milner (1964), fluency tasks are amongst the most widely used clinical neuropsychological tests for the detection of frontal lobe dysfunction. They involve one key executive function, namely the voluntary generation of non-overlearned responses, which is thought to be implemented by the frontal lobes. The Wechsler Adult Intelligence Scale – Performance IQ (WAIS-PIQ; Wechsler, 1997) was used as an alternative measure of fluid intelligence as the subtests in the Performance scale has been shown to load heavily on fluid intelli gence (Kaufman and Lichtenberger, 1999)
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