Neural representation of movement tau
Tan, Heng‐Ru May
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A fundamental aspect of goal‐directed behaviour concerns the closure of motion‐gaps in a timely fashion. An influential theory about how this can be achieved is provided by the tautheory (Lee, 1998). Tau is defined as the ratio of the current distance‐to‐goal gap over the current instantaneous speed towards the goal. In this work we investigated the neural representation of tau in two sets of experiments. In one study we recorded neuromagnetic fluxes (using magnetoencephalography, MEG) from the whole brain of human subjects performing discrete hand movements aimed to targets in space, whereas the other study involved recordings of single cell activity from prefrontal and posterior parietal areas of a behaving monkey during geometrical shape‐copying tasks. These two studies provided complementary information, for the former covered the whole brain (at the cost of weak localization), whereas the latter used the finest neural grain (at the expense of limited brain regions). However, the two studies together yielded valuable information concerning the dynamic, time‐varying neural representation of tau, with respect to both integrated synaptic events in neuronal ensembles (recorded by MEG) and neural spike outputs (recorded by microelectrodes). The relations between neural signals and tau were analyzed using a linear regression model where the time‐varying neural signal (magnetic field strength in fT or spike density function) was the dependent variable and the corresponding value of movement tau and speed were the independent variables. In addition, the model included an autoregressive term to account for the expected correlated errors, given the time series nature of the data. The neurophysiological study revealed a statistically significant (p < 0.05) relation of spike density function to tau (in the presence or absence of a significant speed effect) in 17% of cells in the posterior parietal cortex (N = 399) and 8% of cells in the prefrontal cortex (N = 163). These results are in accord with previous findings in an interception task. The MEG study revealed that a mean of 21.98 (± 6.08) % of sensor signals had a statistically significant (p < 0.05) relation to tau across all subjects. These effects were distributed predominantly over the left parietal‐temporo‐occipital sensor space, with additional foci over the frontal sensorimotor regions. Altogether, these findings demonstrate a specific involvement of neurons and neuronal ensembles with the tau variable and pave the way for further studies on predictive tau control.