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J M Fuster

Publications and source records attributed to J M Fuster.

At least 19 recordsLinked to original sources
PubMed1992

Temporal correlates of information processing during visual short-term memory.

The question is raised whether the sequence of spikes of a cortical neuron, i.e. its spike train, is related to cognitive functions. Neuronal patterns of firing in the inferotemporal cortex of monkeys performing visual delayed-matching tasks showed that short-term memory was accompanied by decreased bursting and changes in the incidence of recurrent spike-interval patterns. The temporal structure of the spike train suggests an inverse relationship between the incidence of repeated patterns and the degree of selectivity of sustained firing frequency elicited by the memorandum (sample stimulus).

Animals↗
PubMed1992

Mnemonic and predictive functions of cortical neurons in a memory task.

Single-neuron discharge was recorded from prefrontal and posterior parietal cortex in monkeys performing a visuo-motor memory task with temporal and spatial separation between cue (color) and directional manual response. During the delay interval between cue and response, neurons in both cortices engaged in two concurrent and reciprocal trends of discharge: (a) sensory-coupled, decelerating firing apparently related to color retention, or (b) motor-coupled, accelerating firing apparently related to the anticipated response direction. In both cortices, the acceleration of the direction-anticipating activity was related to the probability with which the animal could predict, and prepare for, the correct response site. Our findings suggest that neurons from prefrontal and parietal cortex are part of distributed networks, with representational and operational properties, for visuomotor cognitive processing.

Animals↗
PubMed1991

The prefrontal cortex and its relation to behavior.

The prefrontal cortex is critical for temporal organization of behavior. It mediates cross-temporal sensory-motor contingencies, integrating motor action (including speech) with recent sensory information. It performs this role through cooperation of two cognitive functions represented in its dorsolateral areas: short-term memory (STM) and preparatory set. Supporting data have been obtained from monkeys performing delay tasks, which epitomize the principle of cross-temporal contingency. In a given trial, the animal performs an act contingent on a sensory cue given a few seconds or minutes earlier. During the delay between cue and response, cells in dorsolateral prefrontal cortex show sustained activation. Two cell categories can be identified in tasks in which cue and response are spatially separate. Cells of the first participate in STM: Their activation tends to diminish as the delay progresses; in some, the activation level depends on the particular cue received. Similar cells are found elsewhere in cortex. Cells of the second category seem to take part in preparation of motor response: Their activation tends to increase in anticipation of it and may be attuned to the particular movement the cue calls for. This cell type is rare outside of frontal cortex. The temporally integrative function of the prefrontal cortex is probably based on local interactions between "memory" and "motor-set" cells, as well as on neural associations between prefrontal cortex and posterior cortical areas.

Animals↗
PubMed1990

Crossmodal short-term memory of haptic and visual information.

Rhesus monkeys were trained on a within-subjects design to assess whether they could perform concurrently visual-to-haptic (V-H) and haptic-to-visual (H-V) crossmodal delayed matching-to-sample (DMS). A parametric analysis was conducted of the effect of delay between presentation and re-presentation of the test discriminanda (three-dimensional geometric objects). The results indicate that (a) monkeys are capable of concurrent V-H and H-V crossmodal matching of objects by shape, size, and texture; (b) monkeys acquire faster and perform better crossmodal matching in the V-H direction than in the H-V direction; (c) as they learn to perform DMS with successive object pairs, monkeys transfer some--procedural--knowledge from the use of one pair to the use of the next; and (d) in the monkey, crossmodal short-term memory, as measured by DMS performance, has a temporal decline.

Animals↗
PubMed1990

Visual response latencies in temporal lobe structures as a function of stimulus information load.

In a monkey performing a visual delayed matching-to-sample task, units and visual evoked potentials (VEPs) were sampled from the inferior bank of the superior temporal sulcus (STS; Areas TEa and IPa), the hippocampus, and the presubiculum. VEP latencies indicated that flash information--signaling the imminent presentation of a color sample to be retained--reached the presubiculum and the hippocampus substantially earlier than the STS. In contrast, color sample VEP latencies did not differ between sites, arriving at all sites appreciably later than flash VEPs. Unit data indicated generally excitatory responses to both stimuli at all sites and net inhibition during the interstimulus interval separating flash from sample. As with VEPs, unit latencies to flash were shorter than to sample stimuli. The alerting flash data imply activation of the hippocampus occurring before activation of the STS cortex, whereas the coincident arrival of color sample information suggests temporal synchronization between these structures.

Animals↗
PubMed1990

Prefrontal cortex and the bridging of temporal gaps in the perception-action cycle.

Normal behavior is characterized by a constant circular flow of influences from sensory receptors to motor effectors, to the physical environment, back to sensory receptors, and so on. This cybernetic cycle of influences (the perception-action cycle) governs all sequences of behavior to make them adaptive and goal directed. In the primate (including the human primate), considerable evidence indicates that dorsolateral prefrontal cortex is essential for the bridging of temporal gaps in the perception-action cycle, in other words, for mediating cross-temporal contingencies of behavior. This chapter summarizes some neuropsychological and neurophysiological evidence in support of this conclusion. The evidence has been obtained from monkeys performing delay tasks, which epitomize the principle of cross-temporal contingency.

Animals↗
PubMed1990

Inferotemporal units in selective visual attention and short-term memory.

1. This research was designed to further clarify how, in the primate, the neurons of the inferotemporal (IT) cortex support the cognitive functions of visually guided behavior. Specifically, the aim was to determine the role of those neurons in 1) selective attention to behaviorally relevant features of the visual environment and 2) retention of those features in temporary memory. Monkeys were trained in a memory task in which they had to discriminate and retain individual features of compound stimuli, each stimulus consisting of a colored disk with a gray symbol in the middle. A trial began with brief presentation of one such stimulus, the sample for the trial. Depending on the symbol in it, the monkey had to memorize the symbol itself or the background color; after 10-20 s of delay (retention period), two compound stimuli appeared, and the animal had to choose the one with the symbol or with the color of the sample. Thus the test required attention to the symbol, in some trials also to the color, and short-term retention of the distinctive feature for each trial, either a symbol or a color. Single-unit activity was recorded from cortex of the IT convexity, lower and upper banks of the superior temporal sulcus (STS), and from striate cortex (V1). Firing frequency was analyzed during intertrial periods and during the entirety of every trial, except for the (match) choice period. 2. In IT cortex, as in V1, many units responded to the sample stimulus. Some responded indiscriminately to all samples, whereas others responded selectively to one of their features, i.e., to one symbol or to one color. Fifteen percent of the IT units were symbol selective and 21% color selective. These neurons appeared capable of extracting individual features from complex stimuli. Some color cells (color-attentive units) responded significantly more to their preferred color when it was relevant (i.e., had to be retained) than when it was not. 3. The latency of IT-unit response to the sample stimulus was, on the average, relatively short in unselective units (mean 159 ms), longer in symbol units (mean 203 ms), and longest in color-attentive units (mean 270 ms). This order of latencies corresponds to the presumed order of participation of those three types of units in the selective attention to the component features of the sample as required by the task. It suggests intervening steps of serial processing before color information reached color-attentive cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Behavioral electrophysiology of the prefrontal cortex of the primate.

The prefrontal cortex (PFC) is critical for temporal organization of behavior. It mediates cross-temporal sensorimotor contingencies, integrating motor action (including speech) with recent sensory information. It performs this role through cooperation of 2 cognitive functions represented in its dorsolateral areas: short-term memory (STM) and preparatory set. Supporting data have been obtained from monkeys performing delay tasks, which epitomize the principle of cross-temporal contingency. In a given trial, the animal performs an act contingent on a sensory cue given a few seconds or minutes earlier. During the delay between cue and response, cells in dorsolateral PFC show sustained activation. Two cell categories can be identified in tasks in which cue and response are spatially separate. Cells of the first participate in STM: Their activation tends to diminish as the delay progresses; in some, the activation level depends on the particular cue received. Similar cells are found elsewhere in the cortex. Cells of the second category seem to take part in preparation of motor response: Their activation tends to increase in anticipation of it and may be attuned to the particular movement the cue calls for. This cell type is rare outside of the frontal cortex. The temporally integrative function of the PFC is probably based on local interactions between "memory" and "motor-set" cells, as well as on neural associations between PFC and posterior cortical areas.

Animals↗
PubMed1989

Effects of cooling parietal cortex on prefrontal units in delay tasks.

The effects of cooling posterior parietal cortex (areas 5 and 7) on behavior and on the activity of prefrontal neurons were assessed in monkeys performing two visual discrimination tasks with delayed choice. In both tasks, the visual cue for each trial was displayed for 0.5 s by rear projection through colored filters on a central 2.5-cm translucid button. After a variable delay, the choice stimuli were presented on two lower stimulus-response buttons; to obtain a reward, the animal had to press the correct button in accord with the cue. In one task, a red or a green cue called for the choice of that color when the two colors appeared after the delay; in the other task, a yellow or blue cue called for the choice of, respectively, the right or the left of the two white-illuminated choice buttons. Prefrontal single-unit activity (sulcus principalis area) and eye movements were recorded during task performance while parietal areas were at normal or subnormal (6-20 degrees C) temperature. Two-thirds of the units investigated showed significant spontaneous firing changes, most commonly a decrease, as a result of bilateral parietal cooling. A similar proportion of units showed cooling-related changes, excitatory or inhibitory, of their firing activity during the task; such firing changes could occur in any trial-epoch. Parietal cooling also induced misreaching, slow and inaccurate ocular movements, and longer choice reaction time, but did not alter performance in terms of correct responses. Our results suggest the involvement of posterior parietal cortex in spatial aspects of task performance (reaching speed and accuracy, eye movements, reaction time). They also suggest the existence of functional influences from parietal upon prefrontal cortex. Those influences, however, seem not essential for the basic role of the prefrontal cortex in the temporal integration of behavior.

Animals↗
PubMed1989

Unit activity in monkey parietal cortex related to haptic perception and temporary memory.

The neural responses of 456 single units were recorded in parietal cortex of behaving monkeys during a haptic delayed matching-to-sample task. (1) In areas 2 and 5 together, 22% of the neurons were activated by the auditory cue that signalled the beginning of a trial. Virtually all of these cells were also activated during the arm movements required by the task. These neurons, showing both auditory-related and movement-related responses, may function in sensorimotor integration. (2) Responses related to arm projection frequently began before movement onset, sometimes as much as 320 ms before. Such "premovement" responses were approximately equally common, and showed the same latency distribution, in areas 2, 5a, and 5b. (3) There was a topographic rostral-to-caudal gradient of decreasing neural responsiveness to the animal's manipulation of the cue (sample) objects. Eleven percent of manipulation-activated cells responded preferentially to one of the sample objects. (4) Many cells showed sustained (greater than 3 s) activation during the delay period (the time between handling of the sample object and palpation of the choice objects), even though at that time the monkey was sitting quietly and without stimulation. (5) Cells with sustained activation throughout most or all of the 18-s delay period were rare in all areas tested except area 5a. These cells, especially those that were preferentially activated depending on which sample object was palpated, may function in the temporary retention of haptic attributes. (6) The population of cells activated during sample manipulation was largely distinct from the population of cells showing sustained activation during the delay period. These two cell populations may represent different but complementary aspects of haptic perception. (7) The most common response during the delay period was sustained inhibition. This may be an expression of a nonspecific mechanism for decreasing background noise and enhancing neural responses to an anticipated perceptual event. (8) Relatively little evidence was found to support a functional distinction between the neural response properties of areas 2 and 5a. This suggests that area 2 may be at a higher level in the somatosensory hierarchy of the posterior parietal cortex than usually considered.

Acoustic Stimulation↗
PubMed1988

Prefrontal representation of stimulus attributes during delay tasks. I. Unit activity in cross-temporal integration of sensory and sensory-motor information.

The activity of 294 single units was recorded from the dorsolateral prefrontal cortex of monkeys performing two visual discrimination tasks with delayed response. One task, delayed matching-to-sample (DMS), required memory of a colored cue for later (18 s) matching and choice of color; the cue did not connote the location of the delayed response. The other task, delayed conditional position discrimination (DCPD), required memory of a colored cue for later (18 s) choice of spatial response; the cue did connote delayed-response location. All 4 cues (red and green in DMS, yellow and blue in DCPD) were isoluminous and appeared in identical location at trial start. Differential unit reactions to the two DCPD cues were more common than those to the two DMS cues (samples). During the delay period, 15% of all units showed, in one task or the other, differential discharge depending on the cue. In DCPD, a large proportion of the units showing direction-related activity at the time of motor response also reacted with a firing frequency change to one or both (spatially identical) trial-initiating cues. Some units showed coherence of cue-related and response-related changes in accord with the behavioral association between color and direction of response (i.e., yellow-right, blue-left). The reactivity of some units was correlated with the behavioral performance of the tasks in terms of correctness or incorrectness of response. The results indicate that, during visual delay tasks, neurons in the dorsolateral prefrontal cortex may process both spatial and non-spatial information. Because of their protracted differential discharge between cue and response (i.e., during the delay), some units seem involved in the transfer of sensory information across time. These findings suggest the role of prefrontal neurons in the representation of multiple attributes of sensory stimuli, including their associated motor connotations, and the overlap of the cortical representations of different attributes. They are also consistent with the role of the prefrontal cortex in the cross-temporal mediation of sensory-motor contingencies and, therefore, the temporal organization of behavior.

Animals↗
PubMed1988

Prefrontal representation of stimulus attributes during delay tasks. II. The role of behavioral significance.

Rhesus monkeys were trained to perform two visual discrimination tasks with delayed response. In both tasks, the response depended on the color of the cue, a lighted circle in the center of a panel. Red and green guided one task, yellow and blue the other. In the course of performance, a fifth color (violet), non-relevant and inconsequential, was presented at random in the same location as the cues. All 5 stimuli were of equal brightness. Many cells in the dorsolateral prefrontal cortex (sulcus principalis and superior convexity) treated the relevant cues differently than the irrelevant stimulus. In general, cellular reactions to that stimulus were of lesser magnitude than the reactions to the cues. Cell reaction differences as a function of stimulus significance outnumbered and overshadowed differences as a function of cue-color or any other task variable. The results indicate that, during visual delay tasks, units in the dorsolateral prefrontal cortex differentiate stimuli by their behavioral significance, as well as by other stimulus attributes, including color. Because the motivational evaluation of sensory stimuli is an integral part of the cognitive processes in delay tasks (together with short-term memory and motor set), these results support the notion that the prefrontal cortex integrates motivational inputs into the structure of behavioral action.

Animals↗
PubMed1986

[Idiopathic diffuse polyalgia syndrome].

The term "idiopathic diffuse polyalgia syndrome" is suggested to designate an entity well known to neurologists, rheumatologists and all physicians interested in pain. In this syndrome pain is diffuse but often predominates in a given region. Physical examination shows excessive tenderness in well-defined areas. Radiological and laboratory examinations are negative. Psychological factors are not always obvious. Several arguments are in favour of dysfunction of the pain control mechanisms. The effectiveness of the various treatments prescribed is related to the quality of the doctor-patient relation.

Humans↗
PubMed1986

A microelectrode for depth recording in awake animals.

The manufacture is described of a metal, glass-coated microelectrode for single-cell recording from deep structures of the brain during behavioral testing. It is thin, long, and straight, and has excellent electrical properties.

Animals↗
PubMed1985

Functional interactions between inferotemporal and prefrontal cortex in a cognitive task.

Monkeys were trained to perform a visual short-term memory task (delayed matching to sample). In some of the animals, cooling probes were implanted over dorsolateral prefrontal cortex, covering sulcus principalis and adjacent areas; microelectrode pedestals were implanted over inferotemporal cortex. Other animals were fitted with converse implants: cooling probes over a portion of the inferotemporal cortical convexity and microelectrode pedestals over prefrontal cortex. In the awake and behaving monkeys, bilateral cooling of either the prefrontal or the inferotemporal region (to 20 degrees C) induced, in the other region, reversible changes of spontaneous and task-related cell discharge. In the two cortices remote cooling induced augmentations and diminutions of cell reaction to the color samples which the animal had to retain for correct performance of the task. The same was true for cell discharge during the delay, the retention period which followed each sample. However, a net effect of remote cooling was, in both cortices, a diminution of color-dependent differences in the reactions and delay-discharge of some cells. Concomitantly, errors of task-performance increased. Cells that as a result of remote cortical cooling showed changes of reaction to the color samples were found more commonly in supragranular than infragranular layers. The results are interpreted as evidence of mutual influences between inferotemporal and prefrontal areas, probably mediated by corticocortical connections. The single-cell data, together with the behavioral data, suggest that those influences are functionally important for visual discrimination and short-term memory.

Action Potentials↗
PubMed1985

Occipital and inferotemporal responses to visual signals in the monkey.

This study analyzes cellular and field-potential responses in striate and inferotemporal cortex to visual stimuli in monkeys performing a memory task (delayed matching-to-sample). Each trial was initiated by a brief alerting diffuse flash preceding presentation of the memorandum (sample); the latter was a lighted circle (red or green, 1.5 s) to be retained by the animal during a subsequent delay for correct behavioral response (color match). The alerting flash evoked distinct excitatory cell responses and field potentials in the occipital cortex; those two orders of phenomena were broadly related to each other in temporal terms. By contrast, most cells in the inferotemporal region were inhibited by the flash, although the local evoked field potential had a configuration similar to that of the occipital potential. In each region, the sample stimuli elicited excitatory unit responses which summed to a unimodal distribution with an initial component roughly corresponding in time course to the local field potential. Although the shortest response latencies were found in occipital cortex, considerable temporal overlap of the sample-related activities in the two cortices was observed. The finding that most inferotemporal cells, unlike occipital cells, treated only the sample with excitatory response indicates that the inferotemporal cortex is selectively attuned to visual detail. However, the largely simultaneous activation of both cortical regions following the onset of the sample suggests that discriminative visual information is processed by hierarchic interactions of the two cortices through their reciprocal connections.

Animals↗
PubMed1985

The elgiloy microelectrode: fabrication techniques and characteristics.

A glass-insulated microelectrode made from elgiloy orthodontic wire, a stainless cobalt-chromium alloy containing 15% iron, was described by Suzuki and Azuma (1976). Here, we detail a set of modified electrode fabrication procedures, including techniques for hardening and etching the wire, specifying the size, geometry and exposure of the tip, and adjusting tip impedance over a wide range. Accurate insulation of the tip with molten solder glass produces microelectrodes suitable for extracellular recording from single or multiple units and simultaneous recording of evoked potentials. The finished electrode is tough enough to withstand multiple penetrations of the thickened, fibrous dura of the chronic monkey preparation. The iron content allows Prussian blue staining of marking lesions for histological verification of recording sites.

Alloys↗