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A precise form of divisive suppression supports population coding in the primary visual cortex.

MacEvoy SP, Tucker TR, Fitzpatrick D - Nat. Neurosci. (2009)

Bottom Line: The responses of neurons in the primary visual cortex (V1) to an optimally oriented grating are suppressed when a non-optimal grating is superimposed.Using intrinsic signal optical imaging, we found that patterns of tree shrew V1 activity evoked by superimposed equal-contrast gratings were predicted by the averages of patterns evoked by individual component gratings.This prediction held across contrasts, for summed sinusoidal gratings or nonsumming square-wave gratings, and was evident in single-unit extracellular recordings.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA. macevoy@psych.upenn.edu

ABSTRACT
The responses of neurons in the primary visual cortex (V1) to an optimally oriented grating are suppressed when a non-optimal grating is superimposed. Although cross-orientation suppression is thought to reflect mechanisms that maintain a distributed code for orientation, the effect of superimposed gratings on V1 population responses is unknown. Using intrinsic signal optical imaging, we found that patterns of tree shrew V1 activity evoked by superimposed equal-contrast gratings were predicted by the averages of patterns evoked by individual component gratings. This prediction held across contrasts, for summed sinusoidal gratings or nonsumming square-wave gratings, and was evident in single-unit extracellular recordings. Intracellular recordings revealed consistent levels of suppression throughout the time course of subthreshold responses. These results indicate that divisive suppression powerfully governs population responses to multiple orientations. Moreover, the specific form of suppression that we observed appears to support independent population codes for stimulus orientation and strength and calls for a reassessment of mechanisms that underlie cross-orientation suppression.

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Contrast response function derived from a single imaging session in one animal. Each point represents the area under the PRP for a single grating presented at the contrast shown. The area of each PRP was computed by first subtracting the minimum value from each point in that PRP, and then evaluating the integral of a circular Gaussian function fit to the results. Areas were normalized to the maximum across all contrasts. Data are fit with a Naka-Rushton function, with parameters c50 = 0.24±0.13 and n = 1.24±0.35; these compare to values of 0.33 and 1.64, respectively, found with optical imaging in cat V137.
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Figure 7: Contrast response function derived from a single imaging session in one animal. Each point represents the area under the PRP for a single grating presented at the contrast shown. The area of each PRP was computed by first subtracting the minimum value from each point in that PRP, and then evaluating the integral of a circular Gaussian function fit to the results. Areas were normalized to the maximum across all contrasts. Data are fit with a Naka-Rushton function, with parameters c50 = 0.24±0.13 and n = 1.24±0.35; these compare to values of 0.33 and 1.64, respectively, found with optical imaging in cat V137.

Mentions: Though the idea that the shape of the population response represents the stimulus orientation spectrum is fairly conventional, the idea that the total population activity, i.e. the area under the curve of the population response, could provide an independent representation of stimulus intensity has not figured prominently in previous discussions of population coding. However, a role for summed population activity as an independent measure of overall stimulus strength has been featured in at least one model of population-based probabilistic stimulus decoding38. Consistent with this role, we find that plotting PRP area versus contrast of a single grating yields a contrast response function very similar to those of individual neurons (Fig. 7, also see 37). Moreover, the consistency of the component mean in predicting responses to superimposed gratings across contrasts indicates that a similar contrast response function exists for any pair of superimposed gratings, allowing summed population activity to signal the contrasts of more complex stimuli as well.


A precise form of divisive suppression supports population coding in the primary visual cortex.

MacEvoy SP, Tucker TR, Fitzpatrick D - Nat. Neurosci. (2009)

Contrast response function derived from a single imaging session in one animal. Each point represents the area under the PRP for a single grating presented at the contrast shown. The area of each PRP was computed by first subtracting the minimum value from each point in that PRP, and then evaluating the integral of a circular Gaussian function fit to the results. Areas were normalized to the maximum across all contrasts. Data are fit with a Naka-Rushton function, with parameters c50 = 0.24±0.13 and n = 1.24±0.35; these compare to values of 0.33 and 1.64, respectively, found with optical imaging in cat V137.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2875123&req=5

Figure 7: Contrast response function derived from a single imaging session in one animal. Each point represents the area under the PRP for a single grating presented at the contrast shown. The area of each PRP was computed by first subtracting the minimum value from each point in that PRP, and then evaluating the integral of a circular Gaussian function fit to the results. Areas were normalized to the maximum across all contrasts. Data are fit with a Naka-Rushton function, with parameters c50 = 0.24±0.13 and n = 1.24±0.35; these compare to values of 0.33 and 1.64, respectively, found with optical imaging in cat V137.
Mentions: Though the idea that the shape of the population response represents the stimulus orientation spectrum is fairly conventional, the idea that the total population activity, i.e. the area under the curve of the population response, could provide an independent representation of stimulus intensity has not figured prominently in previous discussions of population coding. However, a role for summed population activity as an independent measure of overall stimulus strength has been featured in at least one model of population-based probabilistic stimulus decoding38. Consistent with this role, we find that plotting PRP area versus contrast of a single grating yields a contrast response function very similar to those of individual neurons (Fig. 7, also see 37). Moreover, the consistency of the component mean in predicting responses to superimposed gratings across contrasts indicates that a similar contrast response function exists for any pair of superimposed gratings, allowing summed population activity to signal the contrasts of more complex stimuli as well.

Bottom Line: The responses of neurons in the primary visual cortex (V1) to an optimally oriented grating are suppressed when a non-optimal grating is superimposed.Using intrinsic signal optical imaging, we found that patterns of tree shrew V1 activity evoked by superimposed equal-contrast gratings were predicted by the averages of patterns evoked by individual component gratings.This prediction held across contrasts, for summed sinusoidal gratings or nonsumming square-wave gratings, and was evident in single-unit extracellular recordings.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA. macevoy@psych.upenn.edu

ABSTRACT
The responses of neurons in the primary visual cortex (V1) to an optimally oriented grating are suppressed when a non-optimal grating is superimposed. Although cross-orientation suppression is thought to reflect mechanisms that maintain a distributed code for orientation, the effect of superimposed gratings on V1 population responses is unknown. Using intrinsic signal optical imaging, we found that patterns of tree shrew V1 activity evoked by superimposed equal-contrast gratings were predicted by the averages of patterns evoked by individual component gratings. This prediction held across contrasts, for summed sinusoidal gratings or nonsumming square-wave gratings, and was evident in single-unit extracellular recordings. Intracellular recordings revealed consistent levels of suppression throughout the time course of subthreshold responses. These results indicate that divisive suppression powerfully governs population responses to multiple orientations. Moreover, the specific form of suppression that we observed appears to support independent population codes for stimulus orientation and strength and calls for a reassessment of mechanisms that underlie cross-orientation suppression.

Show MeSH
Related in: MedlinePlus