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Reaching activity in parietal area V6A of macaque: eye influence on arm activity or retinocentric coding of reaching movements?

Marzocchi N, Breveglieri R, Galletti C, Fattori P - Eur. J. Neurosci. (2008)

Bottom Line: The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons.Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically.The majority of V6A reaching neurons use a system that encompasses both of these reference frames.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Fisiologia Umana e Generale, Università di Bologna, I-40126 Bologna, Italy.

ABSTRACT
Parietal area V6A contains neurons modulated by the direction of gaze as well as neurons able to code the direction of arm movement. The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons. To this purpose, we used a visuomotor task in which the direction of arm movement remained constant while the animal changed the direction of gaze. Gaze direction modulated reach-related activity in about two-thirds of tested neurons. In several cases, modulations were not due to the eye-position signal per se, the apparent eye-position modulation being just an epiphenomenon. The real modulating factor was the location of reaching target with respect to the point gazed by the animal, that is, the retinotopic coordinates towards which the action of reaching occurred. Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically. In other neurons, reaching activity is coded spatially, depending on the direction of reaching movement regardless of where the animal was looking at. The majority of V6A reaching neurons use a system that encompasses both of these reference frames. These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.

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Gaze modulation on the transport phase of reaching (epoch MOV): average population behaviour of V6A neurons modulated in MOV. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and MOV epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in MOV but not in FIX epochs. The average SDFs for the preferred (best MOV response) and non-preferred (worst MOV response) conditions are shown as continuous and dashed lines, respectively. Two dotted lines for each SDF indicate the variability band (SEM). The activity of cells in each population was aligned twice (on cue onset and on onset of arm movement, respectively, as indicated by vertical continuous bars). Vertical dashed bar indicates the beginning of FIX. Scale bar in all SDF plots: 0.76.
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fig04: Gaze modulation on the transport phase of reaching (epoch MOV): average population behaviour of V6A neurons modulated in MOV. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and MOV epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in MOV but not in FIX epochs. The average SDFs for the preferred (best MOV response) and non-preferred (worst MOV response) conditions are shown as continuous and dashed lines, respectively. Two dotted lines for each SDF indicate the variability band (SEM). The activity of cells in each population was aligned twice (on cue onset and on onset of arm movement, respectively, as indicated by vertical continuous bars). Vertical dashed bar indicates the beginning of FIX. Scale bar in all SDF plots: 0.76.

Mentions: Figure 4 shows the average behaviour of the V6A task-related cells modulated in MOV epoch. We considered the responses (SDFs) of each neuron in the preferred (continuous curve) and the non-preferred (dashed curve) condition, i.e. the conditions eliciting the best and the worst response, respectively, in MOV epoch. Single neuron responses were normalized and then averaged across the population. Neurons were divided in the three groups, shown in Table 1, based on the type of modulation observed during the fixation interval with respect to MOV epoch: consistent pattern (Bonferroni-corrected t-test, P < 0.05) in FIX and MOV; inconsistent pattern (Bonferroni-corrected t-test, P < 0.05) in FIX and MOV; no eye-position effect in FIX.


Reaching activity in parietal area V6A of macaque: eye influence on arm activity or retinocentric coding of reaching movements?

Marzocchi N, Breveglieri R, Galletti C, Fattori P - Eur. J. Neurosci. (2008)

Gaze modulation on the transport phase of reaching (epoch MOV): average population behaviour of V6A neurons modulated in MOV. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and MOV epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in MOV but not in FIX epochs. The average SDFs for the preferred (best MOV response) and non-preferred (worst MOV response) conditions are shown as continuous and dashed lines, respectively. Two dotted lines for each SDF indicate the variability band (SEM). The activity of cells in each population was aligned twice (on cue onset and on onset of arm movement, respectively, as indicated by vertical continuous bars). Vertical dashed bar indicates the beginning of FIX. Scale bar in all SDF plots: 0.76.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2268963&req=5

fig04: Gaze modulation on the transport phase of reaching (epoch MOV): average population behaviour of V6A neurons modulated in MOV. (A and B) Normalized population responses of V6A neurons showing consistent (A) or inconsistent (B) patterns of modulation in FIX and MOV epochs. (C) Normalized population responses of V6A neurons modulated by gaze direction in MOV but not in FIX epochs. The average SDFs for the preferred (best MOV response) and non-preferred (worst MOV response) conditions are shown as continuous and dashed lines, respectively. Two dotted lines for each SDF indicate the variability band (SEM). The activity of cells in each population was aligned twice (on cue onset and on onset of arm movement, respectively, as indicated by vertical continuous bars). Vertical dashed bar indicates the beginning of FIX. Scale bar in all SDF plots: 0.76.
Mentions: Figure 4 shows the average behaviour of the V6A task-related cells modulated in MOV epoch. We considered the responses (SDFs) of each neuron in the preferred (continuous curve) and the non-preferred (dashed curve) condition, i.e. the conditions eliciting the best and the worst response, respectively, in MOV epoch. Single neuron responses were normalized and then averaged across the population. Neurons were divided in the three groups, shown in Table 1, based on the type of modulation observed during the fixation interval with respect to MOV epoch: consistent pattern (Bonferroni-corrected t-test, P < 0.05) in FIX and MOV; inconsistent pattern (Bonferroni-corrected t-test, P < 0.05) in FIX and MOV; no eye-position effect in FIX.

Bottom Line: The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons.Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically.The majority of V6A reaching neurons use a system that encompasses both of these reference frames.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Fisiologia Umana e Generale, Università di Bologna, I-40126 Bologna, Italy.

ABSTRACT
Parietal area V6A contains neurons modulated by the direction of gaze as well as neurons able to code the direction of arm movement. The present study was aimed to disentangle the gaze effect from the effect of reaching activity upon single V6A neurons. To this purpose, we used a visuomotor task in which the direction of arm movement remained constant while the animal changed the direction of gaze. Gaze direction modulated reach-related activity in about two-thirds of tested neurons. In several cases, modulations were not due to the eye-position signal per se, the apparent eye-position modulation being just an epiphenomenon. The real modulating factor was the location of reaching target with respect to the point gazed by the animal, that is, the retinotopic coordinates towards which the action of reaching occurred. Comparison of neural discharge of the same cell during execution of foveated and non-foveated reaching movements, performed towards the same or different spatial locations, confirmed that in a part of V6A neurons reaching activity is coded retinocentrically. In other neurons, reaching activity is coded spatially, depending on the direction of reaching movement regardless of where the animal was looking at. The majority of V6A reaching neurons use a system that encompasses both of these reference frames. These results are in line with the view of a progressive visuomotor transformation in the dorsal visual stream, that changes the frame of reference from the retinocentric one, typically used by the visual system, to the arm-centred one, typically used by the motor system.

Show MeSH
Related in: MedlinePlus