Responses to task-irrelevant visual features by primate prefrontal neurons.
Lauwereyns, Johan, Masamichi Sakagami, Ken-Ichiro Tsutsui, Shunsuke Kobayashi,
Masashi Koizumi, Okihide Hikosaka.
1Department of Physiology, Juntendo University, Tokyo; 2Brain Science Research
Center, Tamagawa University, Tokyo; 3Department of Physiology, Nihon University,
Tokyo; and 4Department of Neurology, University of Tokyo, Tokyo
APStracts 8:0230J, 2001.
The primate brain is equipped with prefrontal circuits for interpreting visual information,
but how these circuits deal with competing stimulus-response (S-R) associations remains
unknown. Here we show different types of responses to task-irrelevant visual features in
three functionally dissociated groups of primate prefrontal neurons. Two Japanese
macaques participated in a go/no-go task in which they had to discriminate either the
color or the motion direction of a visual target to make a correct manual response. Prior
to the experiment, the monkeys had been trained extensively so that they acquired fixed
associations between visual features and required responses (e.g., "green =
go" "downward motion = no-go"). In this design, the monkey was
confronted with a visual target from which it had to extract relevant information (e.g.,
color in the color-discrimination condition) while ignoring irrelevant information (e.g.,
motion direction in the color-discrimination condition). We recorded from 436 task-
related prefrontal neurons while the monkey performed the multi-dimensional go/no-go
task: 139 (32 %) neurons showed go/no-go discrimination based on color as well as
motion direction ("Integration cells"); 192 neurons (44 %) showed go/no-go
discrimination only based on color ("Color-feature cells"); and 105 neurons
(24 %) showed go/no-go discrimination only based on motion direction ("Motion-
feature cells"). Overall, however, 162 neurons (37 %) were influenced by irrelevant
information: 53 neurons (38 %) among Integration cells, 71 neurons (37 %) among
Color-feature cells, and 38 neurons (36 %) among Motion-feature cells. Across all types
of neurons, the response to an irrelevant feature was positively correlated with the
response to the same feature when it was relevant, indicating that the influence from
irrelevant information is a residual from S-R associations that are relevant in a different
context. Temporal and anatomical differences among Integration, Color-feature and
Motion-feature cells suggested a sequential mode of information processing in prefrontal
cortex, with Integration cells situated toward the output of the decision-making process.
In these cells, the response to irrelevant information appears as a congruency effect, with
better go/no-go discrimination when both the relevant and irrelevant feature are
associated with the same response than when they are associated with different responses.
This congruency effect could be the result of the combined input from Color-feature and
Motion-feature cells. Thus, these data suggest that irrelevant features lead to partial
activation of neurons even toward the output of the decision-making process in primate
prefrontal cortex.
Received 5 March 2001; accepted in final form 21 May 2001
APS Manuscript Number J177-1.
Article publication pending Am J Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 31 July 2001