Neural antecedents of self-initiated actions in secondary motor cortex

Abstract

The neural origins of spontaneous or self-initiated actions are not well understood and their interpretation is controversial. To address these issues, we used a task in which rats decide when to abort waiting for a delayed tone. We recorded neurons in the secondary motor cortex (M2) and interpreted our findings in light of an integration-to-bound decision model. A first population of M2 neurons ramped to a constant threshold at rates proportional to waiting time, strongly resembling integrator output. A second population, which we propose provide input to the integrator, fired in sequences and showed trial-to-trial rate fluctuations correlated with waiting times. An integration model fit to these data also quantitatively predicted the observed inter-neuronal correlations. Together, these results reinforce the generality of the integration-to-bound model of decision-making. These models identify the initial intention to act as the moment of threshold crossing while explaining how antecedent subthreshold neural activity can influence an action without implying a decision.

Robust neuronal dynamics in premotor cortex during motor planning

“…4c). Integrator models with a continuum of fixed points generate ramping activity by integrating their inputs 5,412837 ; these models predict an activity offset compared to the unperturbed trajectories, inconsistent with the data (Extended Data Fig. 1f, g).…”

“…Neurons in frontal and parietal cortex show slow dynamics, including persistent and ramping activity, related to motor planning [1][2][3][4] , action timing 5,6 , working memory [7][8][9][10] and decision making [11][12][13] . Neurons have intrinsic time constants on the order often milliseconds 14 .…”

Spontaneous Decisions and Free Will: Empirical Results and Philosophical Considerations

“…(C ) An M2 neuron that shows negative correlation between the firing rate and the waiting time. The format is the same as is in Figure 3A. (Adapted from Murakami et al 2014. ) by which transient units became correlated with each other, the contribution of each single unit became much more significant, even at large population sizes.…”

“…These signals have been claimed to reflect prior unconscious decisions, raising doubts about the causal role of conscious will. Murakami et al (2014. Nat Neurosci 17: 1574-1582 have recently argued for a different interpretation.…”

“…The central reference will be the recent work of Murakami et al (2014), who presented new experimental evidence about the neural origins of spontaneous decisions in rats. We have taken as our mission the nontrivial task of providing an account accessible to both scientists and philosophers, without doing injustice to either by oversimplification.…”