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Patrizia Fattori, Annalisa Bosco, Rossella Breveglieri, Nicoletta Marzocchi, Claudio Galletti; Visual and somatosensory guidance of reaching movements in the medial parieto-occipital cortex of the macaque. Journal of Vision 2009;9(8):697. doi: 10.1167/9.8.697.
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© ARVO (1962-2015); The Authors (2016-present)
Primates are skillful in reaching targets in their peripersonal space both when they use visual information and when they rely only on somatosensory information. We studied the role of visual and somatosensory guidance of reaching movements by recording single cells in the medial parieto-occipital area V6A, where neurons are modulated by reaching execution in darkness (Fattori et al, 2005), as well as by visual (Galletti et al., 1999) and proprioceptive stimuli (Breveglieri et al., 2002).
A total of 75 units were recorded from V6A in 2 Macaca Fascicularis executing reaching movements towards targets located in different positions. Reaches were performed with the contralateral arm in two conditions: in darkness (Dark) and full light (Light). In Dark, only the reaching target was visible, whereas in Light the monkey also saw its own arm and the environment. The guidance of the arm was merely proprioceptive in Dark, proprioceptive and visual in Light.
We found that 67 out of 75 cells were modulated by reaching execution in at least one spatial position in either background (comparison with baseline activity, t-test, p[[lt]]0.05). A two-way ANOVA (p[[lt]]0.05) was performed (factors: target position, visual background): task-related neurons were 90% (61/67). In about half of them (32/61) the strength of spatial tuning was similar in Light and Dark. A third of neurons (19/61) showed modulations stronger in Light, while a minority (10/61) unexpectedly showed stronger modulations in Dark. V6A population showed a poor coherence of spatial tuning between Dark and Light and some cells showed opposite spatial preferences in Dark and Light.
These data demonstrate that both visual and proprioceptive signals modulate the neural activity in V6A when the arm reaches targets located in the peripersonal space. However, they argue against a simple additive interaction between these signals.
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