2,152 research outputs found
Over-recruitment in the aging brain as a function of task demands: evidence for a compensatory view
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How time modulates spatial responses
No full textBehavioural evidence suggests a left-to-right directionality in the representation of elapsing time. We tested whether this representation produces a spatial attentional shift that activates a corresponding left-to-right spatial response code. Fourteen participants judged whether a cross lasted for a short (1 sec) or a long (2 sec) duration with left and right responses, respectively, or vice versa, while event-related potentials (ERPs) were measured. Responses were faster when participants judged short and long durations with their left and right hand, respectively, than vice versa. In these compatible conditions only (short-left; long-right), ERP negativity developed over the right motor scalp region around the short duration, a finding that is compatible with an early pre-activation of left-hand responses, and over the left motor region around the long duration, suggesting a later pre-activation of right hand responses. These findings confirm that in this task elapsing time is represented from left to right, and that this representation generates corresponding response codes that influence performanc
fMRI investigation of speed-accuracy strategy switching
No full textSwitching between rapid and accurate responses is an important aspect of decision-making. However, the brain mechanisms important to smoothly change the speed-accuracy strategy remain mostly unclear. This issue was addressed here by using functional magnetic resonance imaging (fMRI). On each trial, right-handed healthy participants had to stress speed or accuracy in performing a color discrimination task on a target stimulus according to the instructions given by an initial cue. Participants were capable of trading speed for accuracy and vice versa. Analyses of cue-related fMRI activations revealed a significant recruitment of left middle frontal gyrus and right cerebellum when switching from speed to accuracy. The left superior parietal lobule was activated in the same switching condition but only after the target onset. The anterior cingulate cortex was more recruited, also after target presentation, when speed had to be maintained from one trial to the next. These results are interpreted within a theoretical framework that attributes a role in criterion-setting to the left lateral prefrontal cortex, perceptual evidence accumulation to the superior parietal lobule, and action energization to the anterior cingulate cortex, extending previous findings to the domain of speed-accuracy tradeoff regulation
Effects of focal frontal lesions on response inhibition
No full textThis study examined the performance of 38 normal subjects and 43 patients with focal lesions of the frontal lobes on a simple go-nogo 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
A specific brain structural basis for individual differences in reality monitoring.
No full textMuch recent interest has centered on understanding the relationship between brain structure variability and individual differences in cognition, but there has been little progress in identifying specific neuroanatomical bases of such individual differences. One cognitive ability that exhibits considerable variability in the healthy population is reality monitoring; the cognitive processes used to introspectively judge whether a memory came from an internal or external source (e.g., whether an event was imagined or actually occurred). Neuroimaging research has implicated the medial anterior prefrontal cortex (PFC) in reality monitoring, and here we sought to determine whether morphological variability in a specific anteromedial PFC brain structure, the paracingulate sulcus (PCS), might underlie performance. Fifty-three healthy volunteers were selected on the basis of MRI scans and classified into four groups according to presence or absence of the PCS in their left or right hemisphere. The group with absence of the PCS in both hemispheres showed significantly reduced reality monitoring performance and ability to introspect metacognitively about their performance when compared with other participants. Consistent with the prediction that sulcal absence might mean greater volume in the surrounding frontal gyri, voxel-based morphometry revealed a significant negative correlation between anterior PFC gray matter and reality monitoring performance. The findings provide evidence that individual differences in introspective abilities like reality monitoring may be associated with specific structural variability in the PFC
Fifty Years of Prefrontal Cortex Research: Impact on Assessment
No full textOur knowledge of the functions of the prefrontal cortex, often called executive, supervisory, or control, has been transformed over the past 50 years. After operationally defining terms for clarification, we review the impact of advances in functional, structural, and theoretical levels of understanding upon neuropsychological assessment practice as a means of identifying 11 principles/challenges relating to assessment of executive function. Three of these were already known 50 years ago, and 8 have been confirmed or emerged since. Key themes over this period have been the emergence of the use of naturalistic tests to address issues of "ecological validity"; discovery of the complexity of the frontal lobe control system; invention of new tests for clinical use; development of key theoretical frameworks that address the issue of the role of prefrontal cortex systems in the organization of human cognition; the move toward considering brain systems rather than brain regions; the advent of functional neuroimaging, and its emerging integration into clinical practice. Despite these huge advances, however, practicing neuropsychologists are still desperately in need of new ways of measuring executive function. We discuss pathways by which this might happen, including decoupling the two levels of explanation (information processing; brain structure) and integrating very recent technological advances into the neuropsychologist's toolbox. (JINS, 2017, 23, 755-767)
Self-archiving practice and the influence of publisher policies in the social sciences
No full textAuthors in different disciplines exhibit very different behaviours on the so-called ‘green’ road to open access, i.e. self-archiving. This study looks at the self-archiving behaviour of authors publishing in leading journals in six social science disciplines. It tests the hypothesis that authors are self-archiving according to the norms of their respective disciplines rather than following self-archiving policies of publishers, and that, as a result, they are self-archiving significant numbers of publisher PDF versions. It finds significant levels of
self-archiving, as well as significant self-archiving of
the publisher PDF version, in all the disciplines
investigated. Publishers’ self-archiving policies have
no influence on author self-archiving practice
Delayed inhibition of an anticipatory action during motion extrapolation
No full textBackground: Continuous visual information is important for movement initiation in a variety of motor tasks.
However, even in the absence of visual information people are able to initiate their responses by using motion
extrapolation processes. Initiation of actions based on these cognitive processes, however, can demand more
attentional resources than that required in situations in which visual information is uninterrupted. In the
experiment reported we sought to determine whether the absence of visual information would affect the latency
to inhibit an anticipatory action.
Methods: The participants performed an anticipatory timing task where they were instructed to move in
synchrony with the arrival of a moving object at a determined contact point. On 50% of the trials, a stop sign
appeared on the screen and it served as a signal for the participants to halt their movements. They performed the
anticipatory task under two different viewing conditions: Full-View (uninterrupted) and Occluded-View (occlusion of
the last 500 ms prior to the arrival at the contact point).
Results: The results indicated that the absence of visual information prolonged the latency to suppress the
anticipatory movement.
Conclusion: We suggest that the absence of visual information requires additional cortical processing that creates
competing demand for neural resources. Reduced neural resources potentially causes increased reaction time to
the inhibitory input or increased time estimation variability, which in combination would account for prolonged
latency
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