Salk Institute for Biological Studies
Government Grants Promoting Cruelty to Animals
Salk Institute for Biological Studies, La Jolla, CA
JOHN H. REYNOLDS - Primate Testing - 2006
Grant Number: 5R01EY016161-02
Abstract: DESCRIPTION (provided by applicant): The proposed projects involve making single-unit recording studies in the awake monkey to test a simple cortical circuit model of attention. If supported empirically, the model promises to provide a major simplification in our understanding of the neural mechanisms of spatial attention. At the end of the proposed course of research, we expect to have achieved important and profoundly simplifying insights into the neural mechanisms of attention.
We will have characterized key contrast-dependent response properties of V4, which itself will constitute an important step forward (Aim 1). We will have tested whether these contrast-dependent response properties in Area V4 mirror those of V1 (Aim 1). Understanding any differences that may exist between contrast modulation in V4 and V 1 is important. To the extent that they are similar, this will allow us to establish a mechanistic link between these two important visual processing areas, and to broaden the significance of models of processing in V 1.
We will have tested whether spatial attention modulates center-surround interactions (Aim 2), which has major ramifications for our understanding of earlier studies. For example, single-unit recording studies in V2, V4, MT and TEO have established that when two stimuli appear together within a neuron's classical RF, the response is driven preferentially by the attended stimulus.
The proposed studies will determine whether this pattern occurs as a result of biasing suppressive center-surround interactions at earlier stages. If so, this will support the simple model advanced in this proposal. If not, this would strongly suggest that the selection occurs at the first stage where RFs are large enough to encompass the two stimuli.
Finally, we will have measured the relationship between contrast-dependent center-surround modulations and attentional selection (Aim 3), providing the strongest test yet of the proposal that attention operates by increasing the effective contrast of the attended stimulus.
Taken together, the proposed research promises to provide a much deeper understanding of the cortical circuits that mediate attentional selection, than has been achieved to date.
Thesaurus Terms: attention, neural information processing, space perception, visual cortex, visual field, visual stimulus neuron, neuropsychology, photostimulus Macaca mulatta, behavior test, behavioral /social science research tag, clinical research, human subject, single cell analysis, vision test
Institution: SALK INSTITUTE FOR BIOLOGICAL STUDIES LA JOLLA,
PNAS | March 6, 2007 | vol. 104 | no. 10 | 4165-4169
BIOLOGICAL SCIENCES / NEUROSCIENCE
Stimulus-specific competitive selection in macaque extrastriate visual area V4
Mazyar Fallah*, Gene R. Stoner , and John H. Reynolds*
*Systems Neurobiology Laboratory and Vision Center Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037 Communicated by Robert Desimone, Massachusetts Institute of Technology, Cambridge, MA, January 4, 2007 (received for review February 21, 2006)
Materials and Methods
Electrophysiology. Two adult male monkeys (Macaca mulatta) were implanted with a head holding device and recording chamber, positioned over area V4 using structural MRIs and stereotaxic coordinates. Area V4 was identified by assessing receptive field sizes, topographic organization, and feature selectivity. Electrodes were advanced via multielectrode drives (Mini05, Thomas Recording Inc; EPS, Alpha-Omega Engineering; minimicrodrive, 3NRMD-3A, Crist Instruments). Neuronal signals were recorded using a Multichannel Acquisition Processor (Plexon, Inc). Single neurons were isolated on-line with Rasputin software and off-line with Offline Sorter (Plexon, Inc). Spike times were determined with 1 ms accuracy. Receptive fields were plotted based on responses to a manually controlled flashing bar. Receptive field diameters ranged from 2.2-7.0 of visual arc ("dva", mean: 4.7 dva; standard deviation 1.4 dva). All neurons were tested with a minimum of 20 stimulus repetitions in each experimental condition.
Stimuli and Task. Stimuli were presented on a computer monitor (Sony Trinitron Multiscan, 640 480 resolution, 120 Hz) placed 57 cm from the monkey. Eye position was monitored via infrared eye tracking (ISCAN Model ETL-400, 240 Hz). Experimental control was maintained with Cortex software.
To receive a juice reward, the monkeys had to maintain gaze within 0.75 dva of a 0.25 dva fixation point throughout the entire trial. After maintaining fixation for 200 ms, one of the two surfaces appeared (dot field: 2.75 dva radius, density: 5 dots/dva2, dot size: 0.05 dva, speed of rotation: 50 of rotation/s). Each surface was defined by dots of one of two photometrically equiluminant colors: red, green, or blue. Colors were chosen based on color selectivity, attempting to optimize selectivity across multiple neurons and electrodes.
Similarly, the positioning of the stimulus was optimized to cover as much of the CRFs of the multiple neurons as possible. The color and direction of rotation of the first surface to appear were selected at random, with equal probability. The second surface appeared 750 ms after the first surface. This delayed surface rotated in the direction opposite to that of the first surface and was of the other color. The two surfaces continued rotating for another 750 ms before disappearing.
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