Neurons in area LIP encode perceptual decisions in a perceptual, not oculomotor, frame of reference
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1
University of Pennsylvania, United States
Perceptual decisions require the brain to read out information from sensory cortex to generate a categorical choice. One prominent approach to identify neural substrates of this read-out process has been to use tasks that link the decision to a specific behavioral response and target neurons known to participate in the selection of that response. For example, neurons in the lateral intraparietal cortex (LIP) of monkeys that contribute to oculomotor preparation can encode decisions about the direction of random-dot motion when they are indicated with particular eye movements. However, a weakness of this approach is the inability to identify perceptual processing that is independent of motor planning. Thus, it is unknown if LIP encodes perceptual decisions not linked to specific eye movements, or how decision-related activity in LIP relates to its other sensory and motor properties. To study these issues, we recorded responses from 84 LIP neurons in two monkeys performing a motion-discrimination task that included a flexible association between the direction decision and the eye-movement response. This "colored-target" task required the monkeys to indicate their decision with an eye movement to a target not at a particular location but of a particular color: the monkey was rewarded for looking at the red target following rightward motion, or the green target following leftward motion. One target was always placed in the neuron’s response field, the other 180∘ opposite relative to the motion stimulus. We also controlled the timing of the association by showing the colored targets either before, during, or after motion viewing. This design allowed us to analyze how the encoding process depends on knowledge of the specific sensory-motor mapping. We found that individual LIP neurons encoded three distinct variables at different times during a trial: target color, saccadic choice, and motion direction. Whenever the colored targets appeared, there tended to be a transient response that was selective for target color, regardless of the motion direction or saccadic choice on that trial. In the epoch just prior to the saccadic response, the same LIP neurons encoded the saccadic choice and not just the color of the chosen target or the direction of motion. In addition, during motion viewing many neurons encoded the direction of motion, regardless of when the monkey learned the specific sensory-motor mapping on that trial. Unlike the color- and choice-selective responses, these motion direction-dependent responses were sensitive to the strength of motion in a manner akin to the decision-related signals reported for LIP using tasks with fixed sensory-motor mappings. Moreover, these direction-dependent responses were most affected by errors, further linking them to the perceptual report. The results suggest a general role for LIP in encoding perceptual decisions, even those not linked to a pre-specified oculomotor response.
Conference:
Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010.
Presentation Type:
Poster Presentation
Topic:
Poster session II
Citation:
Bennur
S and
Gold
J
(2010). Neurons in area LIP encode perceptual decisions in a perceptual, not oculomotor, frame of reference.
Front. Neurosci.
Conference Abstract:
Computational and Systems Neuroscience 2010.
doi: 10.3389/conf.fnins.2010.03.00180
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Received:
03 Mar 2010;
Published Online:
03 Mar 2010.
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Correspondence:
Sharath Bennur, University of Pennsylvania, Philadelphia, United States, sharaths@mail.med.upenn.edu