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2-o03 Neuronal representation of visual saliency in the macaqueosterior parietal cortexomohiro Tanaka, Atsushi Fujimoto, Tadashi Ogawa

Graduate School of Medicine, Kyoto University, Kyoto, Japan

salient stimulus (a red target among green distractors) can automatically attractur attention. To examine neural representation of visual saliency, we trainedonkeys to perform a visual search task in which a singleton target was differ-

nt from distractors in color. We manipulated the degree of visual saliency of thearget by independently changing “target-distractor color contrast” and “stimulus-ackground luminance contrast”. For the estimation of the degree of visual saliency,e used saccade latency. Both contrasts can modulate saccade latency (whenne of the contrasts larger, saccade latency became shorter). We found that thesewo contrasts differentially modulated neuronal activity in the posterior parietalortex (PPC). Target-distractor color contrast modulated the late-period activity,hereas stimulus-background luminance contrast modulated the early-period activ-

ty. Thus,these results suggest that visual saliency derived from the different typesf stimulus contrast is represented with different temporal dynamics in the activityf PPC neurons.

oi:10.1016/j.neures.2009.09.1037

2-o04 Primate prefrontal activities reflects competition amongultiple directionally defined choicesei Watanabe1,2, Shintaro Funahashi1

Kokoro Res. Center, Kyoto University Kyoto, Japan; 2 JSPS Res. Fellow,apan

revious research implicates the role of DLPFC in free-choice decision processing,n which subjects themselves select what to act in the absence of external instruc-ions. To elucidate its neural mechanism, we examined primate prefrontal activitiesnder two oculomotor delayed-response tasks; the free-choice and instructed-hoice tasks. In the free-choice (S-ODR) task, monkeys were required to select,n their own, the direction of saccade among 4 directionally defined alternativesresented as multiple visual cues, while in the instructed-choice (ODR) task, theirection of saccade was externally instructed by a single visual cue. We show thaturing S-ODR performances, the competition among cue-responsive neurons withifferent directional preference occurs, thereby generating directional bias relatingo the monkeys’ subsequent decision. We propose that at least 2 of hypotheticalomponents that underlie free choice performances, (1) random neuronal fluctua-ion, (2) influence of past trial history (Haggard, 2008), are reflected in activities ofLPF neurons.

oi:10.1016/j.neures.2009.09.1038

2-o05 Neuronal activity in the primate prefrontal cortex during aetamemory paradigmkio Tanaka1, Shintaro Funahashi1,2

Grad. Sch. of Human & Environmental Std., Kyoto University, Japan;Kokoro Res. Ctr., Kyoto University, Japan

he prefrontal cortex (PFC) is known to play crucial roles in working memory pro-esses. To further understand the functional characteristics of prefrontal neurons,e recorded single-neuron activity from the dorsolateral PFC while a monkey per-

ormed a modified oculomotor working memory task. In this task, the monkey wasometimes allowed to choose whether to take or escape from a memory test (FrCondition) and was sometimes forced to take the test (FoT condition). The propor-ion of correct performance was higher in the FrC condition, suggesting that theonkey used an ability to monitor its own memory state when deciding whether or

ot to take the tests. We observed task-related activities during the cue, delay, andesponse periods. Some of these neurons exhibited differential activation betweenhe trials in which the monkey chose to take the tests and the trials in which the mon-ey chose to escape. Detailed analysis of these activities may lead to some insights

nto the functional roles of prefrontal neurons in the primate memory system.

oi:10.1016/j.neures.2009.09.1039

2-o06 Inactivation of the putamen impairs action value-basedelectionbut not estimation of values during multi-step choice taskn monkeys

anabu Muranishi1, Hitoshi Inokawa1, Hiroshi Yamada2, Minoruimura1

Department of Physiology, Kyoto Prefectural University of Medicine, JapanCenter for Neural Science, New York University, USA

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o examine whether striatal neuron, which is thought to encode action value, con-ributes to reward based-action selection, we injected muscimol (5 �g/�l, 2–3 �l)nto the putamen of a monkey which chose 1 of 3 targets for reward through win-stay-ose-shift policy. Correct choice rates at first (N1), second (N2), third (N3) choicesere 33, 48, 89%, respectively. Once correct button was hit, monkey got another

eward by choosing the known button (R1, 96%). Rates of error trials choosing lastncorrect buttons again in N2, N3 and R1 trials were 2, 5 and 4%, respectively, beforenjection, but increased to 5, 32 and 5%, respectively after inactivation of the puta-

en at anterior commissure level. Monkey could estimate values that did not dependn a choice because behavioral reaction times were changed depending on rewardrobability after injection, too. When a correct button was illuminated in controlask, monkey chose the button without error. These results supported a view thathe putamen is involved selectively and critically in reward-based action selection.

oi:10.1016/j.neures.2009.09.1040

2-o07 Model-based and model-free leaning by striatal neuronsiaochuan Pan, Masamichi Sakagami

Brain Science Institute, Tamagawa University, Japan

he striatum is the major inputs to basal ganglia and receives afferents from nearly allortical areas. One of functions for the striatum is thought to be involved in habitualehavior, and apply model-free learning for effortless and fast action selection. Toest this hypothesis, we recorded neural activity from the striatum when the monkeyerformed a sequential paired-association task with asymmetric reward task. Theonkey learned two sequences of stimuli: A1-B1-C1 and A2-B2-C2. The asymmetric

eward rule was instructed by pairing C1 (or C2) with large (or small) reward blocky block. The monkey also learned associations between new stimuli (e.g. N1, N2)nd B1 or B2. We found striatal neurons can predict reward based on old stimuliA1 and A2) just after C1 and C2 were paired with reward. These neurons canot discriminate two reward conditions based on new stimuli just after reward

nstruction with C1 and C2, but can after directly experiencing new stimulus-rewardontingency. Our results suggest that the striatum can perform model-based likeethod in familiar situations, but only model-free method in novel environments.

oi:10.1016/j.neures.2009.09.1041

2-o08 Prefrontal neurons contribute to temporal filtering in dura-ion discriminationen-ichi Oshio, Atsushi Chiba, Masahiko Inase

Dept Physiol, Kinki Univ Sch of Med, Osaka-Sayama, Japan

t is widely accepted that the prefrontal cortex is a brain area involved in timeerception; however, its functional roles remain unclear. We trained two monkeyso perform a duration-discrimination task, in which two visual cues were presentedonsecutively for different durations ranging from 0.2 to 2.0 s, and subjects were thenequired to choose the longer cue. Our single-unit recording experiments showedhat phasic activity was the most prevailing among responses to the first cue. Peakime of the phasic activity was broadly distributed about 0.8 s after cue onset. Theroad distribution of the peak time would indicate that various filtering durationsad been prepared for estimating cue duration. The most frequent peak time waslose to the time separating cue durations into long and short. The activity with thiseak time might have had a role of filtering in attempted duration discrimination.ur results suggest that the prefrontal cortex contributes to duration discriminationith temporal filtering in the cue period.

oi:10.1016/j.neures.2009.09.1042

2-o09 Frontal-parietal synchrony (phase-locking) in human EEGuring visual searchteven Phillips, Yuji Takeda

The National Institute for Advanced Industrial Science and Technology (AIST),apan

n a monkey study, Buschman and Miller (2007) reported greater frontal-parietaleuronal synchrony in the lower frequency band (22–34 Hz) for conjunctive thaneature visual search, but a reverse effect in a higher frequency band (36–56 Hz). Wexamine whether this difference is also evident in humans using scalp EEG. Analy-is of phase-locking values revealed significantly greater synchronization betweenrontal and parietal electrode pairs in the lower frequency band around 160–480 msost-stimulus for conjunctive search. No significant difference was observed in the

pper frequency band. These results partly correspond to Buschman and Miller2007), suggesting that top-down control of visual attention is mediated by neuronalynchrony.

oi:10.1016/j.neures.2009.09.1043