Abstract
The motor system prepares for movements well in advance of their execution. In the gaze control system, the dynamics of preparatory neural activity have been well described by stochastic accumulation-to-threshold models. However, it is unclear whether this activity has features indicative of a hidden movement command. We explicitly tested whether preparatory neural activity in premotor neurons of the primate superior colliculus has 'motor potential'. We removed downstream inhibition on the saccadic system using the trigeminal blink reflex, triggering saccades at earlier-than-normal latencies. Accumulating low-frequency activity was predictive of eye movement dynamics tens of milliseconds in advance of the actual saccade, indicating the presence of a latent movement command. We also show that reaching a fixed threshold level is not a necessary condition for movement initiation. The results bring into question extant models of saccade generation and support the possibility of a concurrent representation for movement preparation and generation.
Highlights
The ability to interact with the world through movements is a hallmark of the animal kingdom.Movements are usually preceded by a period of planning, when the nervous system makes decisions about the optimal response to a stimulus and programs its execution
When induced during fixation in the absence of any other target, a reflex blink is accompanied by a blink-related eye movement (BREM) – the eyes turn nasally and downward before returning to the original fixation position in a loop-like trajectory (e.g., Rottach et al, 1998)
The results in this study are based on experiments performed in one node, superior colliculus (SC), in a distributed network of brain regions involved in gaze control
Summary
Movements are usually preceded by a period of planning, when the nervous system makes decisions about the optimal response to a stimulus and programs its execution. Such planning behavior is seen in a wide variety of species, including, insects (Fotowat and Gabbiani, 2007; Card and Dickinson, 2008), fish (Preuss et al, 2006), frogs (Nakagawa and Nishida, 2012), and mammals (Hanes and Schall, 1996; Churchland et al, 2006a). Since variability in the onset and rate of accumulation of low-frequency activity is correlated with eventual saccade reaction times (Hanes and Schall, 1996; Ratcliff and Rouder, 1998; Usher and McClelland, 2001), it is thought that this activity primarily dictates when the movement is supposed to be initiated
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