Neural Basis of a Perceptual Decision in the Parietal Cortex (Area LIP) of the Rhesus Monkey

• Published in: Journal of neurophysiology Vol. 86; no. 4; pp. 1916 - 1936
• Main Authors: Shadlen, Michael N, Newsome, William T
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-10-2001
• Subjects: Action Potentials - physiology; Animals; Discrimination (Psychology) - physiology; Electrophysiology; Female; Linear Models; Macaca mulatta; Male; Motion Perception - physiology; Motor Neurons - physiology; Neurons, Afferent - physiology; Parietal Lobe - cytology; Parietal Lobe - physiology; Photic Stimulation; Psychophysics; Saccades - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2001.86.4.1916

  1 Howard Hughes Medical Institute, Department
of Physiology and Biophysics, and Regional Primate Research Center,
University of Washington, Seattle, Washington 98195-7290; and
  2 Howard Hughes Medical Institute and Department
of Neurobiology, Stanford University School of Medicine, Stanford,
California 94305
Shadlen, Michael N. and
William T. Newsome.
Neural Basis of a Perceptual Decision in the Parietal Cortex
(Area LIP) of the Rhesus Monkey. J. Neurophysiol. 86: 1916-1936, 2001. We recorded the activity of single
neurons in the posterior parietal cortex (area LIP) of two rhesus
monkeys while they discriminated the direction of motion in random-dot
visual stimuli. The visual task was similar to a motion discrimination
task that has been used in previous investigations of motion-sensitive
regions of the extrastriate cortex. The monkeys were trained to decide
whether the direction of motion was toward one of two choice targets
that appeared on either side of the random-dot stimulus. At the end of
the trial, the monkeys reported their direction judgment by making an
eye movement to the appropriate target. We studied neurons in LIP that
exhibited spatially selective persistent activity during delayed
saccadic eye movement tasks. These neurons are thought to carry
high-level signals appropriate for identifying salient visual targets
and for guiding saccadic eye movements. We arranged the motion
discrimination task so that one of the choice targets was in the LIP
neuron's response field (RF) while the other target was positioned
well away from the RF. During motion viewing, neurons in LIP altered
their firing rate in a manner that predicted the saccadic eye movement
that the monkey would make at the end of the trial. The activity thus
predicted the monkey's judgment of motion direction. This predictive
activity began early in the motion-viewing period and became
increasingly reliable as the monkey viewed the random-dot motion. The
neural activity predicted the monkey's direction judgment on both easy and difficult trials (strong and weak motion), whether or not the
judgment was correct. In addition, the timing and magnitude of the
response was affected by the strength of the motion signal in the
stimulus. When the direction of motion was toward the RF, stronger
motion led to larger neural responses earlier in the motion-viewing
period. When motion was away from the RF, stronger motion led to
greater suppression of ongoing activity. Thus the activity of single
neurons in area LIP reflects both the direction of an impending gaze
shift and the quality of the sensory information that instructs such a
response. The time course of the neural response suggests that LIP
accumulates sensory signals relevant to the selection of a target for
an eye movement.