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Biomedical subjects

J M Fuster

Publications and source records attributed to J M Fuster.

79 records · Page 5Linked to original sources
PubMedDate not supplied

Spatial and temporal factors in the role of prefrontal and parietal cortex in visuomotor integration.

The effects of reversible lesion--by cooling--of dorsolateral prefrontal and posterior parietal cortex were studied in rhesus monkeys performing a cognitive visuomotor integration task. Correct performance required the use of a learned set of cue-response contingencies, some spatial and some nonspatial; in some cases, the task required the short-term retention, through a delay, of the color of the cue or its implicit response direction. Prefrontal cooling impaired performance of the task regardless of its spatial demands, an effect that increased with delay. Parietal cooling, on the other hand, only impaired performance if the task demanded the processing and retention of spatial information (i.e., if spatial active memory was required). Parietal effects were not related to delay. Both prefrontal and, even more, parietal cooling increased response time in all task contingencies. Thus, the results dissociate the respective contributions of the prefrontal and the posterior parietal cortex to the temporal and spatial aspects of information processing in visuomotor performance. They indicate that posterior parietal areas participate in spatial processing and in active memory of spatial information, whereas prefrontal areas subserve a broader role of visuomotor processing and cross-temporal integration of both spatial and nonspatial information.

Analysis of Variance↗
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Reversible deficit in haptic delay tasks from cooling prefrontal cortex.

The main purpose of this study was to explore the role of dorsolateral prefrontal cortex in skilled and sequential haptic performance. Monkeys were trained to perform a delayed matching-to-sample task that required the memorization of three-dimensional objects perceived either by palpation (haptically) or by sight. At the start of a trial the animal was allowed to touch or view an object, the sample; after a period of delay, during which the object remained out of touch and out of sight, the animal was presented with two side-by-side objects--one of them the sample--for either tactile or visual recognition, and the choice of the sample (correct match) was rewarded. Three variants of the task were used: (1) visual sample, haptic match; (2) haptic sample, visual match; and (3) haptic sample, haptic match. The temporary bilateral cooling of dorsolateral prefrontal cortex to 15 degrees C induced a reversible deficit in performance of all three tasks. Cooling to the same degree a portion of posterior parietal cortex of equivalent size did not significantly alter either performance or reaction time. These findings indicate that the functional integrity of the dorsolateral prefrontal cortex is important for performance of sequential behavior dependent on haptic skill. Further, the results suggest that the role of this cortex in active memory, already well documented for spatially and nonspatially defined visual information, extends also to tactile information and associated motor acts.

Animals↗
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Cortical metabolic activation in humans during a visual memory task.

A delayed match-to-sample (DMS) task of abstract, visual memory was performed during the uptake period of 18F-fluorodeoxyglucose. The increase in glucose uptake of cortical and subcortical regions ("activation") during the DMS task was compared with that during a control, immediate match-to-sample task using positron emission tomography. Both discriminant analysis and paired t tests supported the observation that the dorsolateral prefrontal area underwent the greatest activation, while a factor analysis revealed the functional correlation matrices of the tasks. Activations in the ventral premotor cortex and supramarginal and angular gyri were highly correlated with the change in the dorsolateral prefrontal cortex. The basal forebrain/ventral pole region showed a smaller but independently significant change. The findings support the role of the dorsal prefrontal region in the nonspatial working memory of humans.

Adult↗
PubMedDate not supplied

From perception to action: temporal integrative functions of prefrontal and parietal neurons.

The dorsolateral prefrontal cortex (DPFC) and the posterior parietal cortex (PPC) are anatomically and functionally interconnected, and have been implicated in working memory and the preparation for behavioral action. To substantiate those functions at the neuronal level, we designed a visuomotor task that dissociated the perceptual and executive aspects of the perception-action cycle in both space and time. In that task, the trial-initiating cue (a color) indicated with different degrees of certainty the direction of the correct manual response 12 s later. We recorded extracellular activity from 258 prefrontal and 223 parietal units in two monkeys performing the task. In the DPFC, some units (memory cells) were attuned to the color of the cue, independent of the response-direction it connoted. Their discharge tended to diminish in the course of the delay between cue and response. In contrast, few color-related units were found in PPC, and these did not show decreasing patterns of delay activity. Other units in both cortices (set cells) were attuned to response-direction and tended to accelerate their firing in anticipation of the response and in proportion to the predictability of its direction. A third group of units was related to the determinacy of the act; their firing was attuned to the certainty with which the animal could predict the correct response, whatever its direction. Cells of the three types were found closely intermingled histologically. These findings further support and define the role of DPFC in executive functions and in the temporal closure of the perception-action cycle. The findings also agree with the involvement of PPC in spatial aspects of visuomotor behavior, and add a temporal integrative dimension to that involvement. Together, the results provide physiological evidence for the role of a prefrontal-parietal network in the integration of perception with action across time.

Animals↗
PubMedDate not supplied

Cellular dynamics of network memory.

One example of "emergence" is the development, as a result of neural ontogeny and living experience, of cortical networks capable of representing and retaining cognitive information. A large body of evidence from neuropsychology, electrophysiology and neuroimaging indicates that so-called working memory and long-term memory share the same neural substrate in the cerebral cortex. That substrate consists in a system of widespread, overlapping and hierarchically organized networks of cortical neurons. In this system, any neuron or group of neurons can be part of many networks, and thus many memories. Working memory is the temporary activation of one such network of long-term memory for the purpose of executing an action in the near future. The activation of the network may be brought about by stimuli that by virtue of prior experience are in some manner associated with the cognitive content of the network, including the response of the organism to those stimuli. The mechanisms by which the network stays activated are presumed to include the recurrent re-entry of impulses through associated neuronal assemblies of the network. Consistent with this notion is the following evidence: (1) working memory depends on the functional integrity of cortico-cortical connective loops; and (2) during working memory, remarkable similarities--including "attractor behavior"--have been observed between firing patterns in real cortex and in an artificial recurrent network.

Animals↗