Journal of Neuroscience, Vol 10, 2528-2540, Copyright © 1990 by Society for Neuroscience
Context-dependent responses of primate nucleus basalis neurons in a go/no-go task
RT Richardson and MR DeLong
Departments of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
In previous studies involving monkeys performing behavioral tasks, neurons
in the nucleus basalis frequently had significant changes in discharge rate
when the animal made a movement in response to a sensory stimulus in order
to obtain a reward. To determine whether such responses of basalis neurons
are primarily sensory or motor in nature, the activity of single basalis
neurons was recorded in monkeys performing a go/no-go (GNG) task which
provided a dissociation between sensory and motor neuronal responses. In a
sample of 425 basalis neurons, 326 (77%) had significant changes in firing
in at least one phase of the GNG task. Most of the task-related neurons
(70%) responded in the choice phase in which the animal either made an arm
movement (go condition) or kept its arm motionless (no-go condition) in
order to obtain a water reward. Of 253 neurons that responded in the choice
phase, 88% had changes in firing in the no-go condition that were equal to
or, in some cases, greater than the changes in firing in the go condition.
Therefore, most responses of basalis neurons in the choice phase could not
be specific for the arm movement because they occurred when there was no
arm movement at all. The visual stimulus presented in the choice phase was
also presented earlier on each trial in the cue phase. Although 70% of the
task-related basalis neurons responded in the choice phase, only 5% had
detectable changes in firing in the cue phase. Of 251 neurons responding in
the cue or choice phase, 59% had significantly larger changes in firing in
the choice phase than in the cue phase, whereas only one neuron had a
larger response in the cue phase. Therefore, most responses of basalis
neurons in the choice phase could not be specific for the visual stimulus
because similar responses did not occur when the same stimulus was
presented in the cue phase. These results indicate that the frequent
responses of basalis neurons in the choice phase are neither purely sensory
nor motor in nature, but are highly dependent on the context of the
stimulus or movement. The neuronal responses in the choice phase may
reflect either transient increases in arousal or decision-making processes.
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