Demonstration of a Methodology for Long-Term Tracking of Intracortical Microstimulation-Evoked Perception Thresholds in Rat Somatosensory Cortex.

BACKGROUND

Intracortical microstimulation (ICMS) offers a promising approach for enabling sensory feedback by directly activating neurons within the somatosensory cortex to more fully realize closed-loop neuroprosthetic systems. Despite this potential, questions persist regarding how stable ICMS-evoked responses remain over extended implantation periods.

NEW METHOD: Given the paucity of preclinical tools for examining these temporal patterns, we extended a previously developed rodent nose-poke go/no-go behavioral framework to assess the reliability of ICMS perception thresholds across a 30-week implantation window. Rats implanted with microwire arrays underwent weekly threshold and behavioral-performance assessment, alongside recordings of electrophysiological and electrochemical data to assess correlates of paradigm reliability.

RESULTS

Threshold values initially fell in an exponential-like manner from weeks 5-12 post-implantation before approaching a fitted asymptote of ~1.1 nC/ph per electrode across 10 stimulating electrodes. Thereafter, thresholds remained stable through week 30 in animals retaining detectable percepts. Over this period, behavioral performance stabilized, with animals correctly responding to the conditioned stimulus ~90% of the time. Notably, neither neural recording nor electrochemical properties of the arrays provided a robust, cross-animal explanation for perceptual threshold trends, leaving the underlying mechanism unresolved. Compared with naïve cortical tissue, gene expression profiling of the implanted tissue expressed elevated Gfap and Cd68 alongside reduced NeuN and Bdnf-findings common to prior neuroinflammation studies.

COMPARISON WITH EXISTING

METHODS

This positive-reinforcement rodent paradigm offers a dependable preclinical alternative for long-term ICMS-threshold assessment.

CONCLUSION

Despite sensation loss in two animals, this behavioral framework offers investigational value for chronic ICMS threshold tracking while sensory percepts remain detectable.