Trends in Neurosciences
ForumSpecial Issue: Time in the BrainMillisecond Spike Timing Codes for Motor Control
Section snippets
When a Millisecond Matters: Correlative and Causal Evidence
Correlative evidence that millisecond spike timing differences affect behavior has been shown across a wide range of species and behaviors. Mammalian motor units regularly exhibit doublets and triplets with inter-spike intervals of 5–10 ms; occurrences increase as muscles fatigue, presumably to increase force via central mechanisms [3]. Recent examples show that spike timing correlates with variations in both fast and slow periodic behaviors, or with selection of different behavioral programs (
Why a Millisecond Matters: Motor Codes Interact with System Biomechanics
Intuitively, it would seem that a millisecond could hardly affect muscle force output, as a spike elicits a 40–100 ms force twitch in mammalian striated muscles [3]. Nonetheless, at least three classes of mechanisms enable small timing changes to profoundly alter motor output in vivo: (i) muscle properties, (ii) mechanical feedback, and (iii) biomechanical sensitivities (Figure 1B).
A number of intrinsic muscle force-generating properties (Figure 1B, i) allow small differences in spike timing and
A Diversity, Not a Dichotomy, of Spike Codes
Recent computational, experimental, and analytical innovations emphasize the diversity of motor codes beyond the classic dichotomy of rate versus timing (Figure 2A); both sensory and motor timing codes can differ across many dimensions (Figure 2D). One crucial issue is whether sensory or motor information is encoded by the timing of individual spikes (‘single-spike code’), the relative timing of two spikes (‘inter-spike-interval code’), or more spikes (‘pattern code’). Furthermore, both rate
New Directions in Timing and the Motor System
Our growing appreciation of timing codes raises as many questions as it answers. One challenge is completeness. Most neural recordings sample a (very) limited subset of the signals involved in motor processing, and often from a single anatomical structure. Questions of timing and rate, consistency, and redundancy would benefit from comprehensive recordings of the motor code, especially with spike level resolution, to capture a more complete picture of the motor program. Spiking datasets
Acknowledgements
This work was supported by NIH R01 NS084844 to SJS, NIH R01 EB022872 and NIH R01 NS099375 to SJS and IN, NIH R01 HD046922 and NIH R01 HD090642 to LHT, ARO W911NF-14-1-0396 and NSF CAREER PoLS 1554790 to SS. This work was done while LHT was visiting the Simons Institute for the Theory of Computing, and in part when SJS, SNS, and IN were visiting the Aspen Center for Physics.
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