Biology subjects

Fellows, L.

Publications and source records attributed to Fellows, L..

3 recordsLinked to original sources

bioRxiv2020

Multimodal imaging evidence for the brain basis of cognitive dysfunction in older HIV+ men

ObjectiveThis study used converging methods to define the structural and functional characteristics of the neural substrates underlying variation in cognitive ability in older men with well-controlled HIV infection. MethodsSeventy-six HIV+ men treated with combination antiretrovirals completed attention and inhibitory control tasks tapping different cortico-subcortical circuits while time-locked high-density EEG was acquired. Fifty-four also underwent structural MRI. We investigated relationships between task-evoked EEG responses, cognitive ability and immunocompromise. MRI suggested a subcortical basis for the observed EEG effects. ResultsEEG activity was associated with cognitive ability at later (P300) but not earlier processing stages of both tasks. However, only the P300 evoked by the attention task was associated with past HIV infection severity. Source localization confirmed that the tasks engaged different brain circuits. Thalamus volumes correlated with P300 amplitudes evoked by the attention task, while globus pallidus volumes were related to the P300 in both tasks. InterpretationThis is the first study to combine structural and functional imaging in an overlapping sample to address the neural circuits related to cognitive dysfunction in HIV. Neural substrates of attention were more affected than those supporting inhibitory control. Preliminary evidence suggests these differences may relate to vulnerability of the thalamus to the effects of HIV. Our results suggest high-yield tasks and circuit targets for future work.

neuroscience↗

bioRxiv2019

Neural correlates of evidence and urgency during human perceptual decision-making in dynamically changing conditions

Current models of decision-making assume that the brain gradually accumulates evidence and drifts towards a threshold which, once crossed, results in a choice selection. These models have been especially successful in primate research, however transposing them to human fMRI paradigms has proved challenging. Here, we exploit the face-selective visual system and test whether decoded emotional facial features from multivariate fMRI signals during a dynamic perceptual decision-making task are related to the parameters of computational models of decision-making. We show that trial-by-trial variations in the pattern of neural activity in the fusiform gyrus reflect facial emotional information and modulate drift rates during deliberation. We also observed an inverse-urgency signal based in the caudate nucleus that was independent of sensory information but appeared to slow decisions, particularly when information in the task was ambiguous. Taken together, our results characterize how decision parameters from a computational model (i.e., drift rate and urgency signal) are involved in perceptual decision-making and reflected in the activity of the human brain.

neuroscience↗

bioRxiv2018

Ventromedial prefrontal cortex is not critical for behavior change without external reinforcement

Cue-approach training (CAT) is a novel paradigm that has been shown to induce preference changes towards items without external reinforcements. In the task the mere association of a neutral cue and a speeded button response has been shown to induce a behavioral change lasting months. This paradigm includes several phases whereby after the training of individual items, behavior change is manifested through binary choices of items with similar initial values. Neuroimaging data have implicated the ventromedial prefrontal cortex (vmPFC) during the choice phase of this task. However, it still remains unclear what are the underlying neural mechanisms during training. Here, we sought to determine whether the ventromedial frontal cortex (VMF) is critical for the non-reinforced preference change induced by CAT. For this purpose, eleven participants with focal lesions involving the VMF and 30 healthy age-matched controls performed the CAT. We found that at the individual level, a similar proportion of VMF and healthy participants showed a preference shift following CAT. The VMF group performed similarly to the healthy age-matched control group in the ranking and training phases. As a group the healthy age-matched controls exhibited a behavior change, but the VMF participants as a group did not. We did not find an association between individual lesion patterns and performance in the task. We conclude that a fully intact VMF is not critical to induce non-externally reinforced preference change and suggest potential mechanisms for this novel type of behavioral change.

neuroscience↗