Aep. Villa et al., CHAOTIC DYNAMICS IN THE PRIMATE MOTOR CORTEX DEPEND ON MOTOR PREPARATION IN A DELAYED-POINTING TASK, Cahiers de psychologie cognitive, 17(4-5), 1998, pp. 763-780
This study investigates the influence of motor preparation on the neur
al dynamics of time series generated by simultaneously recorded spike
trains in the primary motor cortex (MI) of two monkeys performing a de
layed-pointing task. A trial consisted of the following: (1) pre parat
ory signal; (2) preparatory period lasting 600, 900, 1200, or 1500 ms;
(3) response signal; and (4) pointing movement to a target light. We
compared single and pairs of time series, with an overall count of mor
e than 800 spikes, during the control period (i.e., before the onset o
f the preparatory signal, n = 120 spike trains) and during the prepara
tory period (n = 111), irrespective of its duration, to investigate th
e existence of ''chaotic'' (i.e., seemingly unpredictable, yet determi
nistic) dynamics in and across paired spike trains. Five neurons were
characterized by the same dynamics in all recording periods out of a t
otal of 20/120 and 14/111 deterministic dynamics observed during the c
ontrol and preparatory periods, respectively. Interestingly, the value
s of the geometric scaling properties of the neural dynamics during th
e preparatory period were distributed over a broader range than during
the control period. This suggests the disruption of a common or neutr
al state of activity by the ongoing motor preparation. However, disreg
arding the recording period, the majority (71%) of all paired time ser
ies, including at least one ''chaotic'' spike train, showed determinis
tic dynamics. Thus, the question is raised whether such dynamics bear
some message, or whether this represents a ''side effect'' of some glo
bal self-organizing dynamics within the cerebral cortex. Changes in th
e temporal structure of MT spike trains induced by motor preparation s
how that novel methods of analysis, based on the dynamical system appr
oach, may help to reveal some principles underlying the organization o
f brain cortical activity in different behavioral states.