Mapping task-switching in frontal cortex through neuropsychological group studies

This paper considers evidence provided by large neuropsychological group studies and meta-analyses of functional imaging experiments on the location in frontal cortex of the subprocesses involved in the carrying out of task-switching paradigms. The function of the individual subprocesses is also considered in the light of analyses of the performance of normal subjects

A unified science of concussion

The etiology, imaging, and behavioral assessment of mild traumatic brain injury (mTBI) are daunting fields, given the lack of a cohesive neurobiological explanation for the observed cognitive deficits seen following mTBI. Although subjective patient self-report is the leading method of diagnosing mTBI, current scientific evidence suggests that quantitative measures of predictive timing, such as visual tracking, could be a useful adjunct to guide the assessment of attention and to screen for advanced brain imaging. Magnetic resonance diffusion tensor imaging (DTI) has demonstrated that mTBI is associated with widespread microstructural changes that include those in the frontal white matter tracts. Deficits observed during predictive visual tracking correlate with DTI findings that show lesions localized in neural pathways subserving the cognitive functions often disrupted in mTBI. Unifying the anatomical and behavioral approaches, the emerging evidence supports an explanation for mTBI that the observed cognitive impairments are a result of predictive timing deficits caused by shearing injuries in the frontal white matter tracts

MEMORY AND COGNITIVE ABILITIES IN UNIVERSITY PROFESSORS:

Professors from the University of California at Berkeley were administered a 90-min test battery of cognitive performance that included measures of reaction time, paired-associate learning, working memory, and prose recall. Age effects among the professors were observed on tests of reaction time, paired-associate memory, and some aspects of working memory. Age effects were not observed on measures of proactive interference and prose recall, though age-related declines are generally observed in standard groups of elderly individuals. The findings suggest that age-related decrements in certain cognitive functions may be mitigated in intelligent, cognitively active individualsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72229/1/j.1467-9280.1995.tb00510.x.pd

Is there a dysexecutive syndrome?

The role of the frontal lobes has often been described as a ‘paradox’ or a ‘riddle’. Ascribed to this region has been the loftiest of functions (e.g. executive; seat of wisdom); others contested that the frontal lobes played no special role. There has also been controversy about the unity or diversity of functions related to the frontal lobes. Based on the analysis of the effects of lesions of the frontal lobes, we propose that there are discrete categories of functions within the frontal lobes, of which ‘executive’ functioning is one. Within the executive category, the data do not support the concept of an undifferentiated central executive/supervisory system. The results are better explained as impairments in a collection of anatomically and functionally independent but interrelated attentional control processes. Evidence for three separate frontal attentional processes is presented. For each process, we present an operational description, the data supporting the distinctiveness of each process and the evidence for impairments of each process after lesions in specific frontal regions. These processes and their coarse frontal localizations are energization—superior medial, task setting—left lateral and monitoring—right lateral. The strength of the findings lies in replication: across different tasks; across different cognitive modalities (e.g. reaction time paradigms, memory); and across different patient groups. This convergence minimizes the possibility that any of the findings are limited to a specific task or to a specific set of patients. Although distinct, these processes are flexibly assembled in response to context, complexity and intention over real time into different networks within the frontal regions and between frontal and posterior regions

Regional frontal injuries cause distinct impairments in cognitive control

Background: Lesions of the frontal lobes may impair the capacity of patients to control otherwise intact cognitive operations in the face of ambiguous sensory input or conflicting possible responses. Objective: To address the question of whether focal lesions in different regions of the frontal lobes produced specific impairments in cognitive control. Methods: We evaluated 42 patients with chronic frontal lesions and 38 control subjects on a modified Stroop test that allowed measurement of reaction times and errors. Planned, stratified analyses permitted identification of discrete frontal lesions that are critical for impaired performance. Results: Lesions of the left ventrolateral region produced an increased number of incorrect responses to distractors. Lesions of a large portion of the right superior medial region, including anterior cingulate, supplementary motor area (SMA), pre-SMA, and dorsolateral areas, caused a slow reaction time and a decreased number of correct responses to targets. Conclusion: Lesions in two distinct frontal regions impair cognitive control for a Stroop task, and the mechanisms of impairment are specific to the region of injury. This is support for a general proposal that the supervisory system is constructed of distinct subsystems

Effects of focal lesions on response inhibition

This study examined the performance of 38 normal subjects and 43 patients with focal lesions of the frontal lobes on a simple go\u2013nogo task where the probability of the nogo stimulus was either 75% or 25%. Patients with lesions to the superior medial parts of the frontal lobes, in particular to the left superior portion of Brodmann area 6 (which includes the supplementary motor areas and the premotor areas for the right hand) had an increased number of false alarms (incorrect responses to the nogo stimulus). These results indicate that area 6 is specifically involved in the inhibition of response. Patients with lesions to the right anterior cingulate (areas 24 and 32) were slower and more variable in their reaction time. These findings could be explained by an inability to sustain stimulus-response contingencies. Lesions to the right ventrolateral prefrontal cortex (Brodmann areas 44, 45, 47) also increased the variability of response, perhaps by disrupting monitoring performance