A spiral attractor network drives rhythmic locomotion

The joint activity of neural populations is high dimensional and complex. One strategy for reaching a tractable understanding of circuit function is to seek the simplest dynamical system that can account for the population activity. By imaging Aplysia’s pedal ganglion during fictive locomotion, here we show that its population wide activity arises from a low-dimensional spiral attractor. Evoking locomotion moved the population into a low-dimensional, periodic, decaying orbit - a spiral – in which it behaved as a true attractor, converging to the same orbit when evoked, and returning to that orbit after transient perturbation. We found the same attractor in every preparation, and could predict motor output directly from its orbit, yet individual neurons’ participation changed across consecutive locomotion bouts. From these results, we propose that only the low-dimensional dynamics for movement control, and not the high-dimensional population activity, are consistent within and between nervous systems

The role of the interstimulus interval in heterosynaptic facilitation in Aplysia californica

1. (1) From a great number of recordings, 16 cases were selected in which heterosynaptic facilitation (HSF) or inhibition (HSI) could be repeated without fatigue of the test or priming responses for a period up to 2 h.2. (2) Eight of these recordings represented unitary, the rest compound EPSPs. The unitary responses could be divided into those which changed their amplitude during HSF or HSI and those which were facilitated or inhibited in an all or nothing fashion by heterosynaptic interference.3. (3) Various interstimulus intervals (ISIs) for the test and the priming stimulation ranging from 250 to 2,000 msec were tested. The interval which produced the highest amplitude of HSF was between 250 and 450 msec (approximately 350 msec) in 15 out of 16 cases. Shorter or longer intervals showed less heterosynaptic facilitation. No differences of the optimal ISI were found in unitary as compared to compound synaptic potentials.4. (4) The interval which was correlated to the longest total duration of HSF was also 350 msec.5. (5) In 2 cells, HSI was found to be strongest and longest when ISIs of 350 msec were used.6. (6) Since in psychological conditioning experiments ISIs of the same magnitude have been found to be optimal, this paper further allows indicating another similarity between HSF and behavioral conditioning.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32859/1/0000236.pd