Cue-period Activity Research Articles

Task relevance modulates the cortical representation of feature conjunctions in the target template

Little is known about the cortical regions involved in representing task-related content in preparation for visual task performance. Here we used representational similarity analysis (RSA) to investigate the BOLD response pattern similarity between task relevant and task irrelevant feature dimensions during conjunction viewing and target template maintenance prior to visual search. Subjects were cued to search for a spatial frequency (SF) or orientation of a Gabor grating and we measured BOLD signal during cue and delay periods before the onset of a search display. RSA of delay period activity revealed that widespread regions in frontal, posterior parietal, and occipitotemporal cortices showed general representational differences between task relevant and task irrelevant dimensions (e.g., orientation vs. SF). In contrast, RSA of cue period activity revealed sensory-related representational differences between cue images (regardless of task) at the occipital pole and additionally in the frontal pole. Our data show that task and sensory information are represented differently during viewing and during target template maintenance, and that task relevance modulates the representation of visual information across the cortex.

Competitor suppresses neuronal representation of food reward in the nucleus accumbens/medial striatum of domestic chicks.

To investigate the role of social contexts in controlling the neuronal representation of food reward, we recorded single neuron activity in the medial striatum/nucleus accumbens of domestic chicks and examined whether activities differed between two blocks with different contexts. Chicks were trained in an operant task to associate light-emitting diode color cues with three trial types that differed in the type of food reward: no reward (S-), a small reward/short-delay option (SS), and a large reward/long-delay alternative (LL). Amount and duration of reward were set such that both of SS and LL were chosen roughly equally. Neurons showing distinct cue-period activity in rewarding trials (SS and LL) were identified during an isolation block, and activity patterns were compared with those recorded from the same neuron during a subsequent pseudo-competition block in which another chick was allowed to forage in the same area, but was separated by a transparent window. In some neurons, cue-period activity was lower in the pseudo-competition block, and the difference was not ascribed to the number of repeated trials. Comparison at neuronal population level revealed statistically significant suppression in the pseudo-competition block in both SS and LL trials, suggesting that perceived competition generally suppressed the representation of cue-associated food reward. The delay- and reward-period activities, however, did not significantly different between blocks. These results demonstrate that visual perception of a competitive forager per se weakens the neuronal representation of predicted food reward. Possible functional links to impulse control are discussed.

Relationship Between Prefrontal Task-Related Activity And Information Flow During Spatial Working Memory Performance

While monkeys performed spatial working memory tasks, cue- (C), delay- (D), and response-period (R) activities or their combinations (CD, CR, DR, CDR) were observed in prefrontal neurons. In the present study, we tried to understand information flow during spatial working memory performances and how each task-related neuron contributed to this process. We first characterized each neuron based on which task-related activity was exhibited and which information ( cue location or saccade direction) each task-related activity represented, then classified these neurons into 9 groups (C, D cue, D sac, CD cue, D cue R cue, D sac R sac, D cue R sac, CD cue R cue and CD cue R sac). Preferred directions were similar between cue- and delay-period activities in CD cue, CD cue R cue, and CD cue R sac, indicating that the directional selectivity of delay- period activity is affected by the directional selectivity of cue-period activity, all of which represented visual information. Preferred directions were also similar between delay- and response-period activities in D cue R cue, CD cue R cue, and D sac R sac, indicating that the directional selectivity of delay-period activity affects the directional selectivity of response- period activity in these neurons. By the comparison of temporal profiles of delay-period activity among these groups, we found (1) cue-period activity could affect directional selectivity of delay-period activity of CD cue and CD cue R cue, (2) cue-period activity of C, CD cue, and CD cue R cue might contribute to the initiation and the maintenance of delay-period activity of CD cue, CD cue R cue, D cue, and D cue R cue, and (3) saccade-related activity of D sac R sac could be affected by delay-period activity of D sac and D sac R sac. These results suggest that the combination of task-related activities, the information represented by each activity, and the temporal profile of delay-period activity are important factors to consider information flow and processing and integration of the information in the prefrontal cortex during spatial working memory processes.

Cue-period activity of monkey prefrontal neurons during a duration-discrimination task

Cue-period activity of monkey prefrontal neurons during a duration-discrimination task

Contributions of prefrontal cue-, delay-, and response-period activity to the decision process of saccade direction in a free-choice ODR task

To examine how the dorsolateral prefrontal cortex (DLPFC) contributes to the decision process of the saccade direction, we recorded single-neuron activity while two monkeys performed two oculomotor delayed-response (ODR) tasks. In an ordinary ODR task, monkeys were required to make a memory-guided saccade to the cue location after a 3-s delay. In a self-selection version of the ODR task (S-ODR), four identical visual cues were presented simultaneously at the cue period, and monkeys were required to make a saccade toward any one of four directions after a 3-s delay. By comparing the same neuron's activity between two tasks, we found (1) neurons having directional cue-period activity in the ODR task did not show directionally selective activity in the S-ODR task, (2) neurons having directional pre-saccadic activity showed highly similar directional preferences in two tasks and exhibited temporal coupling between the onset of pre-saccadic activity and the initiation of saccadic eye movements, (3) neurons with directional delay-period activity in the ODR task exhibited similar directional preferences and showed gradual increase in the strength of the directional selectivity toward the end of the delay period in the S-ODR task. These results suggest that directional delay-period activity contributes to the decision process of the saccade direction in the S-ODR task, while directional cue-period and pre-saccadic activities do not. The gradual increase of the directional selectivity in delay-period activity might correspond to neural correlates of the decision process of the saccade direction in the S-ODR task.

What information is represented by prefrontal neuronal activity?

Working memory is a mechanism for short-term active storage of information and for processing stored information. Although evidence for temporary storage mechanisms of information has been accumulated, little is known about neuronal mechanisms for processing information. To understand how information is processed in the nervous system, we first need to know what information single-neuron activity represents, then examine how represented information by single-neuron activities changes along the temporal sequence of the trial. We used two kinds of culomotor delayed-response (ODR) tasks and examined what information prefrontal single-neuron activity represents. We found that all cue-period activity encoded cue positions. However, among neurons, which exhibited delay-period activity, 86% encoded cue positions, while 13% encoded saccade directions. In addition, among neurons exhibiting oculomotor activity, 58% encoded saccade directions, while 35% encoded cue positions. To visualize temporal patterns of changes of information represented by a population of prefrontal neurons, we analyzed single-neuron activities using a population vector analysis. As a result, we found that information represented by a population of PFC neurons changes gradually during the delay period from information for visual cue to that for saccade.

Postsynaptic current analysis of a model prefrontal cortical circuit for multi-target spatial working memory

The two-layer prefrontal cortical circuit model proposed by Tanaka and Yoshida (Neurocomputing 38–40 (2001) 957) produces cue-period activity in one layer and delay-period activity in the other layer. We have extended this model to have three layers and analyzed the spatio-temporal structures of the postsynaptic currents of neurons representing multiple target locations as well as single target locations. The computer simulation shows the three-dimensional spatio-temporal profiles of the excitatory and inhibitory postsynaptic currents of the pyramidal cells representing multiple target locations in the delay period.

Prefrontal Task-Related Activity Representing Visual Cue Location or Saccade Direction in Spatial Working Memory Tasks

To examine what kind of information task-related activity encodes during spatial working memory processes, we analyzed single-neuron activity in the prefrontal cortex while two monkeys performed two different oculomotor delayed-response (ODR) tasks. In the standard ODR task, monkeys were required to make a saccade to the cue location after a 3-s delay, whereas in the rotatory ODR (R-ODR) task, they were required to make a saccade 90 degrees clockwise from the cue location after the 3-s delay. By comparing the same task-related activities in these two tasks, we could determine whether such activities encoded the location of the visual cue or the direction of the saccade. One hundred twenty one neurons exhibited task-related activity in relation to at least one task event in both tasks. Among them, 41 neurons exhibited directional cue-period activity, most of which encoded the location of the visual cue. Among 56 neurons with directional delay-period activity, 86% encoded the location of the visual cue, whereas 13% encoded the direction of the saccade. Among 57 neurons with directional response-period activity, 58% encoded the direction of the saccade, whereas 35% encoded the location of the visual cue. Most neurons whose response-period activity encoded the location of the visual cue also exhibited directional delay-period activity that encoded the location of the visual cue as well. The best directions of these two activities were identical, and most of these response-period activities were postsaccadic. Therefore this postsaccadic activity can be considered a signal to terminate unnecessary delay-period activity. Population histograms encoding the location of the visual cue showed tonic sustained activation during the delay period. However, population histograms encoding the direction of the saccade showed a gradual increase in activation during the delay period. These results indicate that the transformation from visual input to motor output occurs in the dorsolateral prefrontal cortex. The analysis using population histograms suggests that this transformation occurs gradually during the delay period.

Signal flow in a prefrontal cortical circuit model for working memory loading

The active storage process for working memory, which is substantiated by a specific sustained activity of a population of neurons in the prefrontal cortex, is a circuit property of the cortex. To analyze the circuit mechanisms of this process, we constructed a two-layer prefrontal cortical circuit model. The network with asymmetric inter-laminar connections produces transient, cue-period activity in one layer and delay-period activity in the other layer. The peak firing rate in the delay-period is low enough even though the model neurons do not have NMDA-type channels. The simulation shows that the postsynaptic currents have layer-specific spatio-temporal profiles, which are necessary for the coexistence of the different activity patterns.

Neuronal interactions related to working memory processes in the primate prefrontal cortex revealed by cross-correlation analysis.

To understand neuronal mechanisms for manipulating and/or integrating information in working memory processes, we examined functional interactions among prefrontal neurons exhibiting various task-related activities by cross-correlation analysis. Among 168 neuron pairs isolated, 84 (50%) had significant peaks in cross-correlograms (CCGs); 30 had excitatory central peaks at time 0, 38 had excitatory peaks displaced from time 0, 13 had inhibitory central peaks, and three had both excitatory and inhibitory peaks displaced from time 0. Although significant interactions were observed among prefrontal neurons having various task-related activities, the information flow is present from prefrontal neurons having cue-period activity to neurons having oculomotor activity through neurons having delay-period activity. In addition, neuron pairs both having delay-period activity tended to have significant excitatory peaks in CCGs. Further, neuron pairs that had excitatory central peaks in CCGs tended to have similar directional preferences in task-related activities, and this similarity was the highest in neuron pairs both having cue-period activity. Neuron pairs that had displaced peaks in CCGs also showed similarity in directional preferences in task-related activities, and this similarity was also higher in neuron pairs both having cue-period activity. Interactions between neurons exhibiting task-related activity with different directional preferences increase as the temporal sequence of the task progresses. These results suggest that these interactions play an important role for manipulating and integrating information.

Matching patterns of activity in primate prefrontal area 8a and parietal area 7ip neurons during a spatial working memory task.

Single-unit recording studies of posterior parietal neurons have indicated a similarity of neuronal activation to that observed in the dorsolateral prefrontal cortex in relation to performance of delayed saccade tasks. A key issue addressed in the present study is whether the different classes of neuronal activity observed in these tasks are encountered more frequently in one or the other area or otherwise exhibit region-specific properties. The present study is the first to directly compare these patterns of neuronal activity by alternately recording from parietal area 7ip and prefrontal area 8a, under the identical behavioral conditions, within the same hemisphere of two monkeys performing an oculomotor delayed response task. The firing rate of 222 posterior parietal and 235 prefrontal neurons significantly changed during the cue, delay, and/or saccade periods of the task. Neuronal responses in the two areas could be distinguished only by subtle differences in their incidence and timing. Thus neurons responding to the cue appeared earliest and were more frequent among the task-related neurons within parietal cortex, whereas neurons exhibiting delay-period activity accounted for a larger proportion of task-related neurons in prefrontal cortex. Otherwise, the task-related neuronal activities were remarkably similar. Cue period activity in prefrontal and parietal cortex exhibited comparable spatial tuning and temporal duration characteristics, taking the form of phasic, tonic, or combined phasic/tonic excitation in both cortical populations. Neurons in both cortical areas exhibited sustained activity during the delay period with nearly identical spatial tuning. The various patterns of delay-period activity-tonic, increasing or decreasing, alone or in combination with greater activation during cue and/or saccade periods-likewise were distributed to both cortical areas. Finally, similarities in the two populations extended to the proportion and spatial tuning of presaccadic and postsaccadic neuronal activity occurring in relation to the memory-guided saccade. The present findings support and extend evidence for a faithful duplication of receptive field properties and virtually every other dimension of task-related activity observed when parietal and prefrontal cortex are recruited to a common task. This striking similarity attests to the principal that information shared by a prefrontal region and a sensory association area with which it is connected is domain specific and not subject to hierarchical elaboration, as is evident at earlier stages of visuospatial processing.

Spatial selectivity of go/no-go neurons in monkey prefrontal cortex.

We examined single-unit activity in the inferior prefrontal cortex during a visual go/no-go discrimination task under maintained visual fixation. The monkeys had to base their response on either the color, shape, or position of a discriminative cue, and the relevant task condition was indicated by the color of the fixation spot. We analyzed the spatial selectivity of 128 go/no-go neurons showing a marked differential cue-period activity that depended on whether the stimulus signaled a go or no-go response. Most of these neurons (n = 106, 83%) showed asymmetry between their responses to stimuli in the contralateral and ipsilateral visual fields. Seventy-seven of these neurons had a contralateral preferential field, and 29 had an ipsilateral preferential field. These results show that in many inferior prefrontal neurons a degree of differentiation in their responses to go and no-go stimuli depends on the cue positions, and that the coding of behavioral meaning is carried out mainly in the contralateral hemisphere.

Encoding of behavioral significance of visual stimuli by primate prefrontal neurons: relation to relevant task conditions

Single-unit activity was recorded from the inferior dorsolateral prefrontal cortex of two monkeys while they performed a symmetrically rewarded go/no-go discrimination task. Three different task conditions were used in which the monkeys had to base their response on (1) the color, or (2) the shape, or (3) the position of a cue that was presented during fixation of a light spot. The colors of the fixation spot informed the monkeys which condition was relevant. The monkeys had to make an immediate release (go) or a delayed release (no-go) at the time of the fixation color change (imperative stimulus) depending on the currently relevant condition and the discriminative cue previously presented. The effect of changing the relevant condition on neuronal responses to the discriminative cue was analyzed. Out of 328 neurons tested in two or three conditions, 249 responded differentially at the cue period depending on the particular behavioral meaning of the stimulus (go or no-go) in at least one of the task conditions. This differential cue-period activity was examined across the different task conditions: the majority of neurons (111/154, 72%) showed such activity in all three conditions. In the remaining 43 neurons (28%) the differential activity was observed in two conditions (27/154, 18%) or in one condition (16/154, 10%). A few neurons (n = 7) showed feature-specific cue-period activity. In addition, 27 neurons displayed condition-dependent anticipatory activity prior to the cue onset. It is suggested that neurons in the inferior dorsolateral prefrontal cortex may participate in the conversion of sensory information from different visual channels into behavioral information (information on the upcoming response).