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

Implementation of Office-Based Procedures in Large Institutions

This article discusses the background of office-based procedures in otolaryngology, including definitions of important terms related to office-based procedures. Using a framework of safety, functional logistics, and economics, this article can serve as a guide for how to implement office-based procedures at a large institution

Control of extrinsic feeding muscles in Aplysia

The extrinsic buccal muscles in Aplysia are responsible for the overall protraction and retraction of the buccal mass during feeding. The six pairs of extrinsic muscles are organized into two groups, consisting of three protractors and three retractors. Insights into how the extrinsic muscles are controlled were obtained by examining the organization of the motor neurons that innervated them. The extrinsic buccal muscles are innervated by cerebral ganglion nerves and neurons. All the muscles examined appear to be multiply innervated. Identified neurons in the cerebral B, E, and G clusters were found to be motor neurons for individual extrinsic muscles. Some extrinsic muscles had both excitatory and inhibitory innervation. Two synergistic muscles, the extrinsic ventrolateral protractor (ExVLP) and the extrinsic dorsal protractor (ExDP), had common excitatory innervation by identified neuron E5. Two antagonistic muscles, the ExVLP and the extrinsic ventral retractor (ExVR), also had common innervation. Identified neuron E1 appeared to be an inhibitory motor neuron for the ExVLP but an excitatory motor neuron for the ExVR. Common innervation provides a simple mechanism for coordinating synergistic and antagonistic extrinsic muscles. On the basis of these data, a model for the control of buccal mass protraction and retraction is proposed. Bursting by extrinsic buccal muscles was coordinated with cyclic activity in the intrinsic muscles of the buccal mass. Antagonistic extrinsic muscles burst antiphasically and synergistic extrinsic muscles burst in phase when the buccal mass was fully protracted and exhibited a series of rhythmic contractions. Additionally, cerebral E cluster neurons burst in phase with stereotyped rhythmic buccal motor neuron discharges recorded from buccal nerves. The cerebral E cluster motor neurons were coordinated by common synaptic input. No monosynaptic connections were observed; homologous neurons in each E cluster received synaptic input with similar but not identical timing, indicating that the interneurons that coordinate the homologous motor neurons are synchronized. The source of the rhythm that drives synaptically mediated cerebral extrinsic muscle motor neuron bursting was in the buccal ganglia. Cutting one cerebral-buccal connective eliminated E neuron bursting on that side but had no effect on homologous neurons on the intact side. This suggests that a single oscillator in the buccal ganglia may coordinate both the extrinsic and intrinsic buccal muscles during feeding. </jats:p