Biomedical subjects

Lesley K Fellows

Publications and source records attributed to Lesley K Fellows.

8 recordsLinked to original sources

PubMed2006

Deciding how to decide: ventromedial frontal lobe damage affects information acquisition in multi-attribute decision making.

Ventromedial frontal lobe (VMF) damage is associated with impaired decision making. Recent efforts to understand the functions of this brain region have focused on its role in tracking reward, punishment and risk. However, decision making is complex, and frontal lobe damage might be expected to affect it at other levels. This study used process-tracing techniques to explore the effect of VMF damage on multi-attribute decision making under certainty. Thirteen subjects with focal VMF damage were compared with 11 subjects with frontal damage that spared the VMF and 21 demographically matched healthy control subjects. Participants chose rental apartments in a standard information board task drawn from the literature on normal decision making. VMF subjects performed the decision making task in a way that differed markedly from all other groups, favouring an 'alternative-based' information acquisition strategy (i.e. they organized their information search around individual apartments). In contrast, both healthy control subjects and subjects with damage predominantly involving dorsal and/or lateral prefrontal cortex pursued primarily 'attribute-based' search strategies (in which information was acquired about categories such as rent and noise level across several apartments). This difference in the pattern of information acquisition argues for systematic differences in the underlying decision heuristics and strategies employed by subjects with VMF damage, which in turn may affect the quality of their choices. These findings suggest that the processes supported by ventral and medial prefrontal cortex need to be conceptualized more broadly, to account for changes in decision making under conditions of certainty, as well as uncertainty, following damage to these areas.

Adult↗

PubMed2005

Is anterior cingulate cortex necessary for cognitive control?

Functional neuroimaging studies in normal humans suggest that dorsal anterior cingulate cortex (dACC) plays an important role in cognitive control. This brain area is reliably activated when tasks require the ongoing adjustment of the allocation of attention. The dACC has come to occupy a central role in theories of attention and cognitive control, which hold that dACC either monitors response conflict, signalling the need for adjustments in cognitive processes, or directly mediates such adjustments. However, functional imaging results cannot establish that a brain area is necessary for a particular cognitive process. This requires evidence from loss-of-function studies. Here we assessed cognitive control in four human subjects with damage to dACC and 12 age- and education-matched control subjects using several measures drawn from the functional imaging literature. All four subjects with dACC damage showed normal adjustments in performance following manipulation of response conflict in both Stroop and go-no go tasks. Furthermore, damage to the dACC did not impair the phenomenon of post-error slowing, nor alter the ability to adjust performance in response to explicit speed or accuracy instructions. Thus, cognitive control, as assessed by four different measures in two different tasks, appears to be intact in these subjects, arguing against a necessary role for dACC in this process.

Adult↗

PubMed2005

Dissociable elements of human foresight: a role for the ventromedial frontal lobes in framing the future, but not in discounting future rewards.

Impaired future thinking may be a core aspect of impulsive decision making. Recent efforts to understand the brain processes that underlie impulsivity have suggested a role for the frontal lobes. However, future thinking is unlikely to be a unitary process, and the frontal lobes are not a homogeneous entity. The present study contrasted the effects of dorsolateral and ventromedial frontal lobe damage on two distinct aspects of future thinking in humans. Temporal discounting, the subjective devaluation of reward as a function of delay, is not affected by frontal lobe injury. In contrast, a normal future time perspective (a measure of the length of an individual's self-defined future) depends on the ventromedial, but not dorsolateral, frontal lobes. Furthermore, investigation of the relationship of these two measures with classical symptoms of frontal lobe damage indicates that future time perspective correlates with apathy, not impulsivity. Apathy may deserve more attention in understanding both impaired future thinking and the impaired decision making that may result.

Aged↗

PubMed2005

Method matters: an empirical study of impact in cognitive neuroscience.

A major thrust of cognitive neuroscience is the elucidation of structure-function relationships in the human brain. Over the last several years, functional neuroimaging has risen in prominence relative to the lesion studies that formed the historical core of work in this field. These two methods have different strengths and weaknesses. Among these is a crucial difference in the nature of evidence each can provide. Lesion studies can provide evidence for necessity claims, whereas functional neuroimaging studies do not. We hypothesized that lesion studies will continue to have greater scientific impact even as the relative proportion of such studies in the cognitive neuroscience literature declines. Using methods drawn from systematic literature review, we identified a set of original cognitive neuroscience articles that employed either functional imaging or lesion techniques, published at one of two time points in the 1990s, and assessed the effect of the method used on each article's impact across the decade. Functional neuroimaging studies were cited three times more often than lesion studies throughout the time span we examined. This effect was in large part due to differences in the influence of the journals publishing the two methods; functional neuroimaging studies appeared disproportionately more often in higher impact journals. There were also differences in the degree to which articles using one method cited articles using the other method. Functional neuroimaging articles were less likely to include such cross-method citations.

Brain↗

PubMed2004

Different underlying impairments in decision-making following ventromedial and dorsolateral frontal lobe damage in humans.

Ventromedial prefrontal cortex (VMF) damage can lead to impaired decision-making. This has been studied most intensively with the Iowa gambling task (IGT), a card game that asks subjects to overcome an initial attraction to high-payoff decks as losses begin to accrue. VMF subjects choose from the high risk decks more often than controls, but the fundamental impairments driving poor performance on this complex task have yet to be established. There is also conflicting evidence regarding the role of the dorsolateral prefrontal cortex (DLF) in this task. The present study examined whether poor performance on the IGT was specific for VMF damage and whether fundamental impairments in reversal learning contributed to IGT performance. We found that both VMF and DLF damage leads to impaired IGT performance. The impairment of VMF subjects, but not of DLF subjects, seems to be largely explained by an underlying reversal learning deficit.

Decision Making↗

PubMed2004

The cognitive neuroscience of human decision making: a review and conceptual framework.

Decision making, the process of choosing between options, is a fundamental human behavior that has been studied intensively by disciplines ranging from cognitive psychology to economics. Despite the importance of this behavior, the neural substrates of decision making are only beginning to be understood. Impaired decision making is recognized in neuropsychiatric conditions such as dementia and drug addiction, and the inconsistencies and biases of healthy decision makers have been intensively studied. However, the tools of cognitive neuroscience have only recently been applied to understanding the brain basis of this complex behavior. This article reviews the literature on the cognitive neuroscience of human decision making, focusing on the roles of the frontal lobes, and provides a conceptual framework for organizing this disparate body of work.

Amygdala↗

PubMed2003

Ventromedial frontal cortex mediates affective shifting in humans: evidence from a reversal learning paradigm.

How do the frontal lobes support behavioural flexibility? One key element is the ability to adjust responses when the reinforcement value of stimuli change. In monkeys, this ability--a form of affective shifting known as reversal learning--depends on orbitofrontal cortex. The present study examines the anatomical bases of reversal learning in humans. Subjects with lesions of the ventromedial prefrontal cortex were compared with a group with dorsolateral frontal lobe damage, as well as with normal controls on a simple reversal learning task. Neither form of frontal damage affected initial stimulus-reinforcement learning; ventromedial frontal damage selectively impaired reversal learning.

Adult↗

PubMed2003

Clinical significance of complex repetitive discharges: A case-control study.

Complex repetitive discharges (CRDs) are a striking, infrequent finding on needle electromyography (EMG), but their significance is debated. This retrospective case-control study of 486 patients evaluated in a general hospital-based EMG laboratory examined the association of CRDs with specific diagnostic categories, duration of symptoms, and comorbid diabetes mellitus. No CRDs were identified in patients without other evidence of neuromuscular disease. Myopathy was associated with an increased risk of CRDs (adjusted odds ratio, 5.98; 95% confidence interval, 2.38 to 14.99). In general, neuropathic conditions were not associated with either an increased or decreased risk of CRDs compared with other neuromuscular diseases, although confidence intervals were wide. Similarly, neither the chronicity of symptoms nor the presence of diabetes yielded odds ratios that differed significantly from unity. In clinical populations similar to the one we studied, the positive predictive value of CRDs for any of the diagnoses we evaluated is low. However, the absence of CRDs can be of diagnostic value in that it reduces the likelihood of myopathy or motor neuron disease. The likelihood of finding CRDs in acute conditions is the same as that in chronic conditions.

Case-Control Studies↗