Biomedical subjects

Steven P Wise

Publications and source records attributed to Steven P Wise.

13 recordsLinked to original sources

PubMed2006

Representation of future and previous spatial goals by separate neural populations in prefrontal cortex.

The primate prefrontal cortex plays a central role in choosing goals, along with a wide variety of additional functions, including short-term memory. In the present study, we examined neuronal activity in the prefrontal cortex as monkeys used abstract response strategies to select one of three spatial goals, a selection that depended on their memory of the most recent previous goal. During each trial, the monkeys selected a future goal on the basis of events from the previous trial, including both the symbolic visual cue that had appeared on that trial and the previous goal that the monkeys had selected. When a symbolic visual cue repeated from the previous trial, the monkeys stayed with their previous goal as the next (future) goal; when the cue changed, the monkeys shifted from their previous goal to one of the two remaining locations as their future goal. We found that prefrontal neurons had activity that reflected either previous goals or future goals, but only rarely did individual cells reflect both. This finding suggests that essentially separate neural networks encode these two aspects of spatial information processing. A failure to distinguish previous and future goals could lead to two kinds of maladaptive behavior. First, wrongly representing an accomplished goal as still pending could cause perseveration or compulsive checking, two disorders commonly attributed to dysfunction of the prefrontal cortex. Second, mistaking a pending goal as already accomplished could cause the failures of omission that occur commonly in dementia.

Animals↗

PubMed2006

Neuronal activity related to elapsed time in prefrontal cortex.

We studied prefrontal cortex activity during a saccade task. On each trial, one of three delay periods elapsed between the onset of a visual stimulus and its offset, which triggered a saccade. After stimulus offset, many neurons showed phasic increases in activity that depended on the duration of the preceding delay period. This delay-dependent activity varied only weakly with reaction time and instead appeared to reflect a more general aspect of elapsed time.

Action Potentials↗

PubMed2006

The ventral premotor cortex, corticospinal region C, and the origin of primates.

In addition to its projection to the brainstem, the ventral premotor cortex (PMv) sends axons directly to the upper cervical spinal cord in primates, with few terminations more caudally in either the cervical enlargement or in the lumbosacral spinal segments. This finding suggests that PMv plays a role in the control of head movements. Furthermore, comparative neuroanatomical studies indicate that PMv's corticospinal projection was a primate innovation. If the first primates adapted to an arboreal life that involved unimanual feeding, as some experts believe, then perhaps PMv's corticospinal projection evolved to coordinate head movements with this kind of feeding behavior. The computations underlying such control could later be adapted to control head orientation during social signaling.

Animals↗

PubMed2005

Comparison of population activity in the dorsal premotor cortex and putamen during the learning of arbitrary visuomotor mappings.

A previous study found that as monkeys learned novel mappings between visual cues and responses, neuronal activity patterns evolved at approximately the same time in both the dorsal premotor cortex (PMd) and the putamen. Here we report that, in both regions, the population activity for novel mappings came to resemble that for familiar ones as learning progressed. Both regions showed activity differences on trials with correct responses versus those with incorrect ones. In addition to these common features, we observed two noteworthy differences between PMd and putamen activity during learning. After a response choice had been made, but prior to feedback about the correctness of that choice (reward or nonreward), the putamen showed a sustained activity increase in activity, whereas PMd did not. Also in the putamen, this prereward activity was highly selective for the specific visuomotor mapping that had just been performed, and this selectivity was maintained until the time of the reward. After performance reached an asymptote, the degree of this selectivity decreased markedly to the level typical for familiar visuomotor mappings. These findings support the hypothesis that neurons in the striatum play a pivotal role in associative learning.

Action Potentials↗

PubMed2005

Prefrontal cortex activity related to abstract response strategies.

Many monkeys adopt abstract response strategies as they learn to map visual symbols to responses by trial and error. According to the repeat-stay strategy, if a symbol repeats from a previous, successful trial, the monkeys should stay with their most recent response choice. According to the change-shift strategy, if the symbol changes, the monkeys should shift to a different choice. We recorded the activity of prefrontal cortex neurons while monkeys chose responses according to these two strategies. Many neurons had activity selective for the strategy used. In a subsequent block of trials, the monkeys learned fixed stimulus-response mappings with the same stimuli. Some neurons had activity selective for choosing responses based on fixed mappings, others for choosing based on abstract strategies. These findings indicate that the prefrontal cortex contributes to the implementation of the abstract response strategies that monkeys use during trial-and-error learning.

Action Potentials↗

PubMed2005

Conditional motor learning in the nonspatial domain: effects of errorless learning and the contribution of the fornix to one-trial learning.

Conditional motor learning contributes importantly to behavioral flexibility. In previous work, the authors found that fornix transections impaired the ability of macaque monkeys (Macaca mulatta) to learn conditional motor associations between the nonspatial features of visual stimuli and nonspatially differentiated responses. In the present study, they found that significant 1-trial learning of such associations also depended on the fornix. Furthermore, removal of the hippocampus, subiculum, and subjacent parahippocampal cortex, added to fornix transection, had no effect, thus demonstrating that fornix transections eliminated the contribution of the hippocampal system. In addition, the authors examined the effect of errorless learning and found, in control monkeys, that errors made prior to the 1st correct response retarded 1-trial learning.

Animals↗

PubMed2004

Representation of attended versus remembered locations in prefrontal cortex.

A great deal of research on the prefrontal cortex (PF), especially in nonhuman primates, has focused on the theory that it functions predominantly in the maintenance of short-term memories, and neurophysiologists have often interpreted PF's delay-period activity in the context of this theory. Neuroimaging results, however, suggest that PF's function extends beyond the maintenance of memories to include aspects of attention, such as the monitoring and selection of information. To explore alternative interpretations of PF's delay-period activity, we investigated the discharge rates of single PF neurons as monkeys attended to a stimulus marking one location while remembering a different, unmarked location. Both locations served as potential targets of a saccadic eye movement. Although the task made intensive demands on short-term memory, the largest proportion of PF neurons represented attended locations, not remembered ones. The present findings show that short-term memory functions cannot account for all, or even most, delay-period activity in the part of PF explored. Instead, PF's delay-period activity probably contributes more to the process of attentional selection.

Action Potentials↗

PubMed2004

What, if anything, is the medial temporal lobe, and how can the amygdala be part of it if there is no such thing?

Should the medial temporal lobe (MTL) of primates--which includes allocortical structures such as the hippocampus, neocortical structures such as the parahippocampal cortex, and nuclear structures such as the basolateral amygdala--be considered a single "thing"? According to the prevailing view, here termed the reification theory, the answer is yes. According to this theory, the MTL functions as an amalgamated entity that provides the neuronal mechanisms for declarative memory; the greater the damage to the MTL or any of its components, the greater the deleterious effects on declarative memory. A countervailing view, here called the balkanization theory, holds that the various components of the MTL process and store different kinds of information. According to this theory, damage to each part of the MTL causes a unique set of behavioral deficits-some involving memory, others involving perception, and yet others involving response selection. The empirical neuropsychological evidence favors the balkanization theory, as do some new concepts in theoretical neuroanatomy.

Amygdala↗

PubMed2004

Viewing and doing: similar cortical mechanisms for perceptual and motor learning.

Historically, different groups of researchers have investigated the mechanisms of perceptual learning and motor learning. For sensory cortex, neurophysiological and psychophysical findings have linked changes in perception with altered neuronal tuning properties. However, less information has been forthcoming from motor cortex. This review compares recent findings on perceptual and motor learning, and suggests that similar mechanisms govern both. These mechanisms involve changes in both the center of neuronal tuning functions and their width or slope. The former reflects the values of the sensory or motor parameters that a neuron encodes, and the latter adjusts the encoding sensitivity. These similarities suggest that specific unifying principles for neural coding and computation exist across sensory and motor domains.

Animals↗

PubMed2004

Comparison of learning-related neuronal activity in the dorsal premotor cortex and striatum.

Previous studies have reported learning-related changes in neuronal activity during conditional visuomotor learning, also known as arbitrary sensorimotor mapping, conditional visual discrimination, and symbolic or endogenous mapping. Qualitatively similar observations have been reported for the dorsal premotor cortex, the supplementary eye field, the prefrontal cortex, the hippocampus, the striatum and the globus pallidus. The fact that cells in both the dorsal premotor cortex (PMd) and the basal ganglia show changes in activity during associative learning enables a test of the hypothesis that cortex and basal ganglia function in distributed architectures known as cortical-basal ganglionic modules or 'loops'. We reasoned that if these loops represent functional entities, as proposed, then learning-related changes in activity should occur simultaneously in both the cortical and striatal nodes of a loop. The present results confirmed this prediction; as monkeys learned conditional visuomotor associations, neurons in the premotor cortex and associated parts of the putamen changed their rates at approximately the same time. For the largest number of neurons, the evolution in neural activity occurred in close correspondence to the monkeys' learning curves. As a population, however, learning-related changes in activity continued after the monkeys reached an asymptote in performance.

Action Potentials↗

PubMed2003

Chronic, multisite, multielectrode recordings in macaque monkeys.

A paradigm is described for recording the activity of single cortical neurons from awake, behaving macaque monkeys. Its unique features include high-density microwire arrays and multichannel instrumentation. Three adult rhesus monkeys received microwire array implants, totaling 96-704 microwires per subject, in up to five cortical areas, sometimes bilaterally. Recordings 3-4 weeks after implantation yielded 421 single neurons with a mean peak-to-peak voltage of 115 +/- 3 microV and a signal-to-noise ratio of better than 5:1. As many as 247 cortical neurons were recorded in one session, and at least 58 neurons were isolated from one subject 18 months after implantation. This method should benefit neurophysiological investigation of learning, perception, and sensorimotor integration in primates and the development of neuroprosthetic devices.

Action Potentials↗

PubMed2002

Fornix transection impairs conditional visuomotor learning in tasks involving nonspatially differentiated responses.

Rhesus monkeys learned a series of conditional visuomotor associations involving two-dimensional "objects" that instructed one of three responses: tapping a touch screen, steady contact with the screen for a brief period, or steady contact for a longer period. Relative to controls, fornix-transected monkeys were impaired in the acquisition of new associations and in the retention of preoperatively learned ones. These findings challenge the view that the hippocampal system participates in associative learning only when spatial information is relevant to either the stimulus or the response.

Animals↗

PubMed2002

Interaction of ventral and orbital prefrontal cortex with inferotemporal cortex in conditional visuomotor learning.

Five rhesus monkeys (Macaca mulatta) were trained to learn novel conditional visuomotor associations, to perform this task with familiar stimuli, and to perform a visual matching-to-sample task with the same familiar stimuli. Removal of the orbital and ventral prefrontal cortex (PFv+o) in 1 hemisphere and inferotemporal cortex (IT) in the other, thus completing a surgical disconnection of these 2 regions, yielded an impairment on all 3 tasks. Addition of a premotor cortex lesion to the hemisphere containing the PFv+o lesion did not worsen the impairments. The results indicate that PFv+o interacts with IT in both the learning and retention of conditional visuomotor associations. In addition to those associations, which might be considered lower order rules for choosing a response, frontotemporal interaction also appears to be important for higher order rules, such as those involved in the matching task.

Animals↗