Neurointerface with oscillator motifs for inhibitory effect over antagonist muscles

Abstract

The effect of inhibitory management is usually underestimated in artificial control systems, using biological analogy. According to our hypothesis, the muscle hypertonus could be effectively compensated via stimulation by bio-plausible patterns. We proposed an approach for the compensatory stimulation device as implementation of previously presented architecture of the neurointerface, where (1) the neuroport is implemented as a DAC and stimulator, (2) neuroterminal is used for neurosimulation of a set of oscillator motifs on one-board computer. In the set of experiments with five volunteers, we measured the efficacy of motor neuron inhibition via the antagonist muscle or nerve stimulation registering muscle force with and without antagonist stimulation. For the agonist activation, we used both voluntary activity and electrical stimulation. In the case of stimulation of both the agonist and the antagonist muscles and nerves, we experimented with delays between muscle stimulation in the range of 0-20 ms. We registered the subjective discomfort rate. We did not identify any significant difference between the antagonist muscle and nerve stimulation in both voluntary activity and electrical stimulation of cases showing agonist activity. We determined the most effective delay between the stimulation of the agonist and the antagonist muscles and nerves as 10-20 ms.

Keywords: compensation; neurointerface; neuromodulation; neuroprosthesis; neurosimulation; neurostimulation; oscillator motif; spastic syndrome.

Figure 1

The setup of the neurointerface for muscle stimulation and muscle force recording. (A) (1) Fasteners, (2) the clamp, (3) the upper plate, (4) the volunteer's hand, (5) the lower plate, and (6) the dynamometer; (B) the setup of the neurointerface where NT is the neuroterminal and NP is the neuroport; and (C) the diagram of stimulation: (1) activated muscles and nerve, (2) placement of electrodes [the antagonist muscle (flexor) inhibits the extensor via reflex arc]; and (D) the timeline of the study.

Figure 2

(A) The diagram of the circuit that produces neuronal activity to trigger the muscle/nerve. This circuit is used for the generation of activity in a spiking neural network. We used a three-layered OM network with a 20-Hz stimulation of the first group of neurons in the first layer. Outputs arrive on the motoneurons of the muscles—extensor carpi ulnaris and flexor carpi ulnaris. (B1) The produced spiking activity with a delay of extensor activity generation 10 ms relative to the flexor. The extensor muscle activity starts after the flexor activity. There are two impulses per 100 ms, which indicate 20-Hz impulses (B2). The produced spiking activity with a delay of extensor activity generation 0 ms relative to flexor. Both the muscles are active at the same time. (C) The modulation of 2 kHz. Every impulse should be reset to zero voltage every 0.5 ms.

Figure 3

(A) The extensor muscle force with voluntary activity and during antagonist muscle stimulation (inhibitory effect). (B) The extensor muscle force with voluntary activity and during the ulnar nerve stimulation. (C) The extensor muscle force before antagonist muscle stimulation and during antagonist muscle stimulation (inhibitory effect) with the range of delays. (D) The extensor muscle force before antagonist nerve stimulation and during the ulnar nerve stimulation that innervates the flexor and triggers Ia afferent of the flexor, with the range of delays.

Figure 4

(A) The discomfort rate with the extensor and flexor muscle stimulation. (B) The discomfort rate with the extensor muscle and the ulnar nerve stimulation.

Figure 5

(A) The extensor muscle force difference between voluntary activity and during antagonist muscle stimulation (inhibitory effect), where the green boxplot reflects the delta for both genders of volunteers (women and men) and pink reflects the delta for women and blue for men. (B) The extensor muscle force difference between voluntary activity and during the ulnar nerve stimulation (inhibitory effect). (C) The extensor muscle force difference between before antagonist muscle stimulation and during antagonist muscle stimulation (inhibitory effect) with the range of delays. (D) The extensor muscle force difference before antagonist nerve stimulation and during the ulnar nerve stimulation that innervates the flexor and triggers Ia afferent of the flexor, with the range of delays.