The Largest Response Component in the Motor Cortex Reflects Movement Timing but Not Movement Type

Abstract

Neural activity in monkey motor cortex (M1) and dorsal premotor cortex (PMd) can reflect a chosen movement well before that movement begins. The pattern of neural activity then changes profoundly just before movement onset. We considered the prediction, derived from formal considerations, that the transition from preparation to movement might be accompanied by a large overall change in the neural state that reflects when movement is made rather than which movement is made. Specifically, we examined “components” of the population response: time-varying patterns of activity from which each neuron’s response is approximately composed. Amid the response complexity of individual M1 and PMd neurons, we identified robust response components that were “condition-invariant”: their magnitude and time course were nearly identical regardless of reach direction or path. These condition-invariant response components occupied dimensions orthogonal to those occupied by the “tuned” response components. The largest condition-invariant component was much larger than any of the tuned components; i.e., it explained more of the structure in individual-neuron responses. This condition-invariant response component underwent a rapid change before movement onset. The timing of that change predicted most of the trial-by-trial variance in reaction time. Thus, although individual M1 and PMd neurons essentially always reflected which movement was made, the largest component of the population response reflected movement timing rather than movement type.

Brain-machine interface cursor position only weakly affects monkey and human motor cortical activity in the absence of arm movements

“…2d analysis: the electrode had to modulate during the movement task, which we defined as a firing rate change between the very start of the trial and a subsequent time window where the movement was being made. This test is motivated by the observation that the largest neural response component during arm movement tasks is a general change of firing rates when initiating a movement 53 . Specifically, for each electrode we binned spike counts in two windows during each trial (0 to 150 ms and 150 to 300 ms after target on) and compared these windows’ distributions; electrodes with a significant change (p < 0.01, sign-rank test) were considered ‘task-modulated’.…”

Neural Manifolds for the Control of Movement

“…In this view, the time-dependent activity of individual neurons is simply a reflection of the latent variables (Fig. 1B) (Kaufman et al, 2016; Kobak et al, 2016; Macke et al, 2011). Consider the neural space in Fig.…”

“…The concept of the neural manifold and its associated latent variables has been used in a series of recent studies that replace the search for movement representation by single neurons to consider instead movement planning and execution based on the activation of a few neural modes (Ahrens et al, 2012; Bruno et al, 2015; Churchland et al, 2012, 2010a, 2010b; Churchland and Shenoy, 2007; Elsayed et al, 2016; Kaufman et al, 2016, 2014; Michaels et al, 2016; Overduin et al, 2015; Sadtler et al, 2014; Santhanam et al, 2009; Sussillo et al, 2015). …”

Inferring single-trial neural population dynamics using sequential auto-encoders

“…The Maze task is a variant of a center-out delayed reach task, whose details have previously been described [17]. Briefly, monkey J made arm movements in a 2-dimensional workspace while the position of the right index and middle fingertips was tracked optically.…”

“…For reaction time prediction, we used a largely unsupervised method previously described in [18]. Briefly, for each of the single-session models and the multi-session model, we performed demixing principal components analysis [20] on the factor outputs.…”