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Saccade-induced image motion cannot account for post-saccadic enhancement of visual processing in primate MST.

Cloherty SL, Crowder NA, Mustari MJ, Ibbotson MR - Front Syst Neurosci (2015)

Bottom Line: Primates use saccadic eye movements to make gaze changes.In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards.However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision.

View Article: PubMed Central - PubMed

Affiliation: National Vision Research Institute, Australian College of Optometry Carlton, VIC, Australia ; Department of Optometry and Vision Sciences, Australian Research Council Centre of Excellence for Integrative Brain Function, University of Melbourne Parkville, VIC, Australia ; Department of Electrical and Electronic Engineering, University of Melbourne Parkville, VIC, Australia.

ABSTRACT
Primates use saccadic eye movements to make gaze changes. In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards. How does this enhancement arise-from an internal mechanism associated with saccade generation or through visual mechanisms activated by the saccade sweeping the image of the visual scene across the retina? Spontaneous activity in MSTd is elevated even after saccades made in darkness, suggesting a central mechanism for post-saccadic enhancement. However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision. Like neural responses in MSTd, initial ocular following eye speed is enhanced after saccades, with evidence suggesting both internal and visually mediated mechanisms. Here we recorded from visual neurons in MSTd and measured responses to motion stimuli presented soon after saccades and soon after simulated saccades-saccade-like displacements of the background image during fixation. We found that neural responses in MSTd were enhanced when preceded by real saccades but not when preceded by simulated saccades. Furthermore, we also observed enhancement following real saccades made across a blank screen that generated no motion signal within the recorded neurons' receptive fields. We conclude that in MSTd the mechanism leading to post-saccadic enhancement has internal origins.

No MeSH data available.


Related in: MedlinePlus

Post-saccadic enhancement of neural responses and ocular following eye speed. (A) Representative neural responses from a single MSTd neuron for test stimuli delivered after real saccades. Responses for the short-delay condition (blue) are significantly enhanced compared to those for the long-delay condition (gray). (B) Responses from the same neuron for the same test stimulus delivered after simulated saccades. There is no evidence of enhancement of neural responses after simulated saccades. In both (A,B) the raster plots show responses for the short-delay condition. (C,D) Representative ocular following eye speeds for the same test speed for which the recordings in (A,B) were obtained. Ocular following eye speed is significantly enhanced in the short-delay condition compared to the long-delay condition following both real (C) and simulated (D) saccades. In all panels, solid lines show the average across all trials of a given condition and the shaded regions indicate ±1 SE, estimated by bootstrapping.
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Figure 2: Post-saccadic enhancement of neural responses and ocular following eye speed. (A) Representative neural responses from a single MSTd neuron for test stimuli delivered after real saccades. Responses for the short-delay condition (blue) are significantly enhanced compared to those for the long-delay condition (gray). (B) Responses from the same neuron for the same test stimulus delivered after simulated saccades. There is no evidence of enhancement of neural responses after simulated saccades. In both (A,B) the raster plots show responses for the short-delay condition. (C,D) Representative ocular following eye speeds for the same test speed for which the recordings in (A,B) were obtained. Ocular following eye speed is significantly enhanced in the short-delay condition compared to the long-delay condition following both real (C) and simulated (D) saccades. In all panels, solid lines show the average across all trials of a given condition and the shaded regions indicate ±1 SE, estimated by bootstrapping.

Mentions: Figure 2A shows neural responses from a single cell for both the long- (300 ms, gray) and short-delay (50 ms, blue) conditions. For this cell neural responses to test stimuli delivered soon after real saccades (i.e., the short-delay condition) were significantly enhanced (Figure 2A; ASL = 0.01). In contrast, neural responses to the test stimuli were unchanged following simulated saccades (Figure 2B; ASL = 0.41). Moreover, there was no significant difference in the responses for the long-delay condition following real as opposed to simulated saccades (ASL = 0.4). This is representative of the cells in the broader population. In total we tested 145 MSTd neurons from two monkeys, although not all cells were tested in all conditions (hence the differing cell counts in the population data presented below). We found no significant difference between animals for any of the conditions tested (rank sum tests, P > 0.05). In all cases, cells from both animals were therefore combined and analyzed as a single population. Figures 3A,B show neural responses averaged across all cells, for both the long- and short-delay conditions, using the same conventions as in Figure 2. Figure 3C shows responses averaged across all cells for test stimuli delivered after real saccades made over a blank screen.


Saccade-induced image motion cannot account for post-saccadic enhancement of visual processing in primate MST.

Cloherty SL, Crowder NA, Mustari MJ, Ibbotson MR - Front Syst Neurosci (2015)

Post-saccadic enhancement of neural responses and ocular following eye speed. (A) Representative neural responses from a single MSTd neuron for test stimuli delivered after real saccades. Responses for the short-delay condition (blue) are significantly enhanced compared to those for the long-delay condition (gray). (B) Responses from the same neuron for the same test stimulus delivered after simulated saccades. There is no evidence of enhancement of neural responses after simulated saccades. In both (A,B) the raster plots show responses for the short-delay condition. (C,D) Representative ocular following eye speeds for the same test speed for which the recordings in (A,B) were obtained. Ocular following eye speed is significantly enhanced in the short-delay condition compared to the long-delay condition following both real (C) and simulated (D) saccades. In all panels, solid lines show the average across all trials of a given condition and the shaded regions indicate ±1 SE, estimated by bootstrapping.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4555012&req=5

Figure 2: Post-saccadic enhancement of neural responses and ocular following eye speed. (A) Representative neural responses from a single MSTd neuron for test stimuli delivered after real saccades. Responses for the short-delay condition (blue) are significantly enhanced compared to those for the long-delay condition (gray). (B) Responses from the same neuron for the same test stimulus delivered after simulated saccades. There is no evidence of enhancement of neural responses after simulated saccades. In both (A,B) the raster plots show responses for the short-delay condition. (C,D) Representative ocular following eye speeds for the same test speed for which the recordings in (A,B) were obtained. Ocular following eye speed is significantly enhanced in the short-delay condition compared to the long-delay condition following both real (C) and simulated (D) saccades. In all panels, solid lines show the average across all trials of a given condition and the shaded regions indicate ±1 SE, estimated by bootstrapping.
Mentions: Figure 2A shows neural responses from a single cell for both the long- (300 ms, gray) and short-delay (50 ms, blue) conditions. For this cell neural responses to test stimuli delivered soon after real saccades (i.e., the short-delay condition) were significantly enhanced (Figure 2A; ASL = 0.01). In contrast, neural responses to the test stimuli were unchanged following simulated saccades (Figure 2B; ASL = 0.41). Moreover, there was no significant difference in the responses for the long-delay condition following real as opposed to simulated saccades (ASL = 0.4). This is representative of the cells in the broader population. In total we tested 145 MSTd neurons from two monkeys, although not all cells were tested in all conditions (hence the differing cell counts in the population data presented below). We found no significant difference between animals for any of the conditions tested (rank sum tests, P > 0.05). In all cases, cells from both animals were therefore combined and analyzed as a single population. Figures 3A,B show neural responses averaged across all cells, for both the long- and short-delay conditions, using the same conventions as in Figure 2. Figure 3C shows responses averaged across all cells for test stimuli delivered after real saccades made over a blank screen.

Bottom Line: Primates use saccadic eye movements to make gaze changes.In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards.However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision.

View Article: PubMed Central - PubMed

Affiliation: National Vision Research Institute, Australian College of Optometry Carlton, VIC, Australia ; Department of Optometry and Vision Sciences, Australian Research Council Centre of Excellence for Integrative Brain Function, University of Melbourne Parkville, VIC, Australia ; Department of Electrical and Electronic Engineering, University of Melbourne Parkville, VIC, Australia.

ABSTRACT
Primates use saccadic eye movements to make gaze changes. In many visual areas, including the dorsal medial superior temporal area (MSTd) of macaques, neural responses to visual stimuli are reduced during saccades but enhanced afterwards. How does this enhancement arise-from an internal mechanism associated with saccade generation or through visual mechanisms activated by the saccade sweeping the image of the visual scene across the retina? Spontaneous activity in MSTd is elevated even after saccades made in darkness, suggesting a central mechanism for post-saccadic enhancement. However, based on the timing of this effect, it may arise from a different mechanism than occurs in normal vision. Like neural responses in MSTd, initial ocular following eye speed is enhanced after saccades, with evidence suggesting both internal and visually mediated mechanisms. Here we recorded from visual neurons in MSTd and measured responses to motion stimuli presented soon after saccades and soon after simulated saccades-saccade-like displacements of the background image during fixation. We found that neural responses in MSTd were enhanced when preceded by real saccades but not when preceded by simulated saccades. Furthermore, we also observed enhancement following real saccades made across a blank screen that generated no motion signal within the recorded neurons' receptive fields. We conclude that in MSTd the mechanism leading to post-saccadic enhancement has internal origins.

No MeSH data available.


Related in: MedlinePlus