PubMed Health⌕ Search

Biomedical subjects

Masamichi Sakagami

Publications and source records attributed to Masamichi Sakagami.

9 recordsLinked to original sources
PubMed2007

Functional differences between macaque prefrontal cortex and caudate nucleus during eye movements with and without reward.

The prefrontal cortex and the basal ganglia form mutually connected networks and are thought to play essential roles together in guiding goal-directed behaviors. Yet, these structures seem to have independent pathways to motor outputs as well, suggesting differential contributions to goal-directed behaviors. We hypothesized that the prefrontal cortex guides actions to a direction required by external demands and the basal ganglia guide actions to an internally motivated direction. To test this hypothesis, we used a task in which monkeys were required to make a memory-guided saccade to a direction indicated by a visual cue while only one direction was associated with reward. We observed a functional dissociation between the lateral prefrontal cortex (LPFC), which commonly represented the cue direction, and the caudate nucleus (CD), which commonly represented the reward-associated direction. Furthermore, cue-directed and reward-directed signals were integrated differently in the two areas; when the cue direction and the reward direction were opposite, LPFC neurons maintained tuning to the cue direction, whereas CD neurons lost the tuning. Different types of spatial tuning in the two brain areas may contribute to different types of goal-directed behavior.

Analysis of Variance↗
PubMed2006

Influences of rewarding and aversive outcomes on activity in macaque lateral prefrontal cortex.

Both appetitive and aversive outcomes can reinforce animal behavior. It is not clear, however, whether the opposing kinds of reinforcers are processed by specific or common neural mechanisms. To investigate this issue, we studied macaque monkeys that performed a memory-guided saccade task for three different outcomes, namely delivery of liquid reward, avoidance of air puff, and feedback sound only. Animals performed the task best in rewarded trials, intermediately in aversive trials, and worst in sound-only trials. Most task-related activity in lateral prefrontal cortex was differentially influenced by the reinforcers. Aversive avoidance had clear effects on some prefrontal neurons, although the effects of rewards were more common. We also observed neurons modulated by both positive and negative reinforcers, reflecting reinforcement or attentional processes. Our results demonstrate that information about positive and negative reinforcers is processed differentially in prefrontal cortex, which could contribute to the role of this structure in goal-directed behavior.

Analysis of Variance↗
PubMed2006

Behavioral inhibition and prefrontal cortex in decision-making.

Every day we make innumerable decisions; some require no effort at all whereas others require considerable deliberation and weighing of various options. Despite the importance of decision-making in our lives and increased research interest, the specific neural mechanisms underlying decision-making remain unclear. We propose that the brain has at least two cortical pathways that independently generate a decision about appropriate behavior in given circumstances. These two pathways are extensions of the dorsal and ventral streams of the visual processing pathways. The parieto-premotor (extended dorsal) pathway makes decisions about motor actions in a largely autonomous and automatic fashion whereas the temporo-ventrolateral prefrontal (extended ventral) pathway is involved primarily in deliberate decisions and inhibitory control over behavior through the inhibitory function of the ventrolateral prefrontal cortex.

Animals↗
PubMed2006

Increasing distractor strength improves accuracy.

Attention enhances task-relevant signals while filtering task-irrelevant signals; however, this selection process is not perfect. It is generally assumed that the stronger the irrelevant signal, the more strongly performance is disrupted. The effect of irrelevant coherent motion signals on performance on a color-discrimination task was systematically examined. Motion direction was either congruent or incongruent with response selection. Performance was most impaired when motion signal strength was just above perceptual threshold and improved when the motion signal strength increased. These results suggest that distractors of higher strength increase attentional modulation and are filtered before they interfere with task performance.

Adolescent↗
PubMed2005

Functional significance of delay-period activity of primate prefrontal neurons in relation to spatial working memory and reward/omission-of-reward expectancy.

The lateral prefrontal cortex (LPFC) is important in cognitive control. During the delay period of a working memory (WM) task, primate LPFC neurons show sustained activity that is related to retaining task-relevant cognitive information in WM. However, it has not yet been determined whether LPFC delay neurons are concerned exclusively with the cognitive control of WM task performance. Recent studies have indicated that LPFC neurons also show reward and/or omission-of-reward expectancy-related delay activity, while the functional relationship between WM-related and reward/omission-of-reward expectancy-related delay activity remains unclear. To clarify the functional significance of LPFC delay-period activity for WM task performance, and particularly the functional relationship between these two types of activity, we examined individual delay neurons in the primate LPFC during spatial WM (delayed response) and non-WM (reward-no-reward delayed reaction) tasks. We found significant interactions between these two types of delay activity. The majority of the reward expectancy-related neurons and the minority of the omission-of-reward expectancy-related neurons were involved in spatial WM processes. Spatial WM-related neurons were more likely to be involved in reward expectancy than in omission-of-reward expectancy. In addition, LPFC delay neurons observed during the delayed response task were not concerned exclusively with the cognitive control of task performance; some were related to reward/omission-of-reward expectancy but not to WM, and many showed more memory-related activity for preferred rewards than for less-desirable rewards. Since employing a more preferred reward induced better task performance in the monkeys, as well as enhanced WM-related neuronal activity in the LPFC, the principal function of the LPFC appears to be the integration of cognitive and motivational operations in guiding the organism to obtain a reward more effectively.

Animals↗
PubMed2002

Coding and monitoring of motivational context in the primate prefrontal cortex.

The prefrontal cortex is involved in acquiring and maintaining information about context, including the set of task instructions and/or the outcome of previous stimulus-response sequences. Most studies on context-dependent processing in the prefrontal cortex have been concerned with such executive functions, but the prefrontal cortex is also involved in motivational operations. We thus wished to determine whether primate prefrontal neurons show evidence of representing the motivational context learned by the monkey. We trained monkeys in a delayed reaction task in which an instruction cue indicated the presence or absence of reward. In random alternation with no reward, the same one of several different kinds of food and liquid rewards was delivered repeatedly in a block of approximately 50 trials, so that reward information would define the motivational context. In response to an instruction cue indicating absence of reward, we found that neurons in the lateral prefrontal cortex not only predicted the absence of reward but also represented more specifically which kind of reward would be omitted in a given trial. These neurons seem to code contextual information concerning which kind of reward may be delivered in following trials. We also found prefrontal neurons that showed tonic baseline activity that may be related to monitoring such motivational context. The different types of neurons were distributed differently along the dorsoventral extent of the lateral prefrontal cortex. Such operations in the prefrontal cortex may be important for the monkey to maximize reward or to modify behavioral strategies and thus may contribute to executive control.

Animals↗
PubMed2002

Feature-based anticipation of cues that predict reward in monkey caudate nucleus.

A subset of caudate neurons fires before cues that instruct the monkey what he should do. To test the hypothesis that the anticipatory activity of such neurons depends on the context of stimulus-reward mapping, we examined their activity while the monkeys performed a memory-guided saccade task in which either the position or the color of a cue indicated presence or absence of reward. Some neurons showed anticipatory activity only when a particular position was associated with reward, while others fired selectively for color-reward associations. The functional segregation suggests that caudate neurons participate in feature-based anticipation of visual information that predicts reward. This neuronal code influences the general activity level in response to visual features without improving the quality of visual discrimination.

Animals↗
PubMed2002

Influence of reward expectation on visuospatial processing in macaque lateral prefrontal cortex.

The lateral prefrontal cortex (LPFC) has been implicated in visuospatial processing, especially when it is required to hold spatial information during a delay period. It has also been reported that the LPFC receives information about expected reward outcome. However, the interaction between visuospatial processing and reward processing is still unclear because the two types of processing could not be dissociated in conventional delayed response tasks. To examine this, we used a memory-guided saccade task with an asymmetric reward schedule and recorded 228 LPFC neurons. The position of the target cue indicated the spatial location for the following saccade and the color of the target cue indicated the reward outcome for a correct saccade. Activity of LPFC was classified into three main types: S-type activity carried only spatial signals, R-type activity carried only reward signals, and SR-type activity carried both. Therefore only SR-type cells were potentially involved in both visuospatial processing and reward processing. SR-type activity was enhanced (SR+) or depressed (SR-) by the reward expectation. The spatial discriminability as expressed by the transmitted information was improved by reward expectation in SR+ type. In contrast, when reward information was coded by an increase of activity in the reward-absent condition (SR- type), it did not improve the spatial representation. This activity appeared to be involved in gaze fixation. These results extend previous findings suggesting that the LPFC exerts dual influences based on predicted reward outcome: improvement of memory-guided saccades (when reward is expected) and suppression of inappropriate behavior (when reward is not expected).

Animals↗