Neuronal Representation of Object Choice in the Striatum of the Monkey.

Satoshi Nonomura,Kazuyuki Samejima

doi:10.3389/fnins.2019.01283

Satoshi Nonomura, Kazuyuki Samejima

Open Access

https://doi.org/10.3389/fnins.2019.01283

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Abstract

According to a widely held view, the decision-making process can be conceptualized as a two-step process: “object choice,” which does not include physical actions, followed by “movement choice,” in which action is executed to obtain the object. Accumulating evidence in the field of decision neuroscience suggests that the cortico-basal ganglia circuits play a crucial role in decision-making. However, the underlying mechanisms of the object and movement choices remain poorly understood, mainly because the two processes occur simultaneously in most experiments. In this study, to uncover the neuronal basis of object choice in the striatum, the main input site of the basal ganglia, we designed a behavioral task in which the processes of object and movement choice were temporally separated, and recorded the single-unit activity of phasically active neurons (PANs) (n = 375) in the striatum of two monkeys. We focused our study mainly on neuronal representation during the object choice period, before movement choice, using a mutual information analysis. Population striatal activities significantly represented the information of the chosen object during the object choice period, which indicated that the monkeys actually made the object choice during the task. For the activity of each individual neuron during the object choice period, we identified offered object- and chosen object-type neurons, corresponding to pre- and post-decision signals, respectively. We also found the movement-type neurons during the movement period after the object choice. Most offered object- or chosen object-type neurons were not overlapped with movement-type neurons. The presence of object choice-related signals independent of movement signal in the striatum indicated that the striatum was part of the site where object choice was made within a cortico-basal ganglia circuit.

Highlights

We often make decisions among abstract outcomes without undertaking physical actions
The transition of the mean optimal choice ratio in the choice task across blocks indicated that the optimal choice ratio in both color-reward and shape-reward blocks increased after block change, whereas the optimal choice ratio corresponding to the previous block decreased in both monkeys (Figure 2A left)
To study neuronal representation in relation to object choice, which does not include physical action, in the striatum, we designed a behavioral task, in which object choice could be temporally dissociated from movement choice, and trained two monkeys in the task (Figures 1, 2)

Summary

Introduction

We often make decisions among abstract outcomes without undertaking physical actions. You can decide on the sushi topping before reaching your hand toward the sushi on the dish carried by conveyor belt. In this case, the first step, which does not include the physical action (reaching your hand), could be regarded as the “object choice”; it is followed by the second step, the “movement choice,” in which an action is executed to obtain the object when the object is conveyed in front of you. Several neuroscientists have discussed the concept and neuronal mechanism of the consecutive two-step decision processes (Samejima and Doya, 2007; Padoa-Schioppa, 2011; Cisek, 2012; Chen and Stuphorn, 2015).

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