Linear model of peripheral nerve after surgical manipulation: preliminary report in animal study and model shift

Degeneration Of Spinal Ganglion And Segmental Apparatus Of The Spinal Neurons In Sciatic Nerve Injury: An Experimental Study

Objective — To investigate the extent of degenerative changes in neurons of spinal ganglion and segmental apparatus in various injuries to sciatic nerve in the experiment on white rats. Material and Methods — The research involved 40 white non-pedigree male rats distributed among four groups. The animals of Group 1 (n=10) underwent the compression of nerve trunks with Mosquito clamp forceps for 15 minutes. In Group 2 (n=10), the animals had their nerve trunks ligated; and in Group 3, they had their nerves completely transected in their middle thirds. The separate group of control animals (n=10) suffered no damage to their sciatic nerves. Spinal cords and spinal ganglia at L4-L6 level were the material for histopathological examination. We calculated the number (percent) of degenerated neurons in spinal cords and spinal ganglia at the affected sides on Day 30, and compared them to those at the intact sides. Results — The number (percent) of degenerated neurons in spinal cord and spinal ganglion, expressed as Me (Q1; Q2), constituted 2.52% (1.92; 2.74) and 3.75% (2.37; 4.74) in Group 1, 9.27% (9.03; 9.94) and 16.74% (16.01; 18.22) in Group 2, 25.59% (24.36; 26.29) and 31.94% (31.44; 33.03) in Group 3, respectively. Depending on the number (percent) of degenerated neurons, we classified three grades of change manifestation: mild (Group 1), medium (Group 2), and severe (Group 3). No degenerated neurons were found in the control animals. Conclusion — The compression, ischemic exposure on the sciatic nerve, and complete anatomical transection of its trunk resulted in Wallerian degeneration, as well as degeneration of segmental apparatus in spinal cord neurons.

Electrical stimulation-based nerve location prediction for cranial nerve VII localization in acoustic neuroma surgery

INTRODUCTION

Cranial nerve (CN) VII localization is a critical step during acoustic neuroma surgery because the nerve is generally hidden due to the tumor mass. The patient can suffer from Bell's palsy if the nerve is accidentally damaged during tumor removal. Surgeons localize CN VII by exploring the target area with a stimulus probe. Compound muscle action potentials (CMAPs) are elicited when the probe locates the nerve. However, false positives and false negatives are possible due to unpredictable tissue impedance in the operative area. Moreover, a single CMAP amplitude is not correlated with probe-to-nerve distance.

OBJECTIVES

This paper presents a new modality for nerve localization. The probe-to-nerve distance is predicted by the proposed nerve location prediction model.

METHODS

Input features are extracted from CMAP responses, tissue impedance, and stimulus current. The tissue impedance is calculated from the estimated resistance and capacitance of the tissue equivalent circuit. In this study, experiments were conducted in animals. A frog's sciatic nerve and gastrocnemius were used to represent CN VII and facial muscle in humans, respectively. Gelatin (2.8%) was used as a mock material to mimic an acoustic neuroma. The %NaCl applied to the mock material was used to emulate uncontrollable impedance of tissue in the operative area.

RESULTS

The 10-fold cross-validation results revealed an average prediction accuracy of 86.71% and an average predicted error of 0.76 mm compared with the measurement data.

CONCLUSION

The proposed nerve location prediction model could predict the probe-to-nerve distance across various impedances of the mock material.

Peripheral nerve function estimation by linear model of multi-CMAP responses for surgical intervention in acoustic neuroma surgery

Nerve function assessments are crucial for surgical intervention during acoustic neuroma surgery. Cranial nerves such as acoustic and facial nerves, can be possibly damaged during tumor dissection. Proper surgical intervention should prevent neurological deficit and achieve total tumor removal. Conventionally, nerve function is qualitatively evaluated by surgeon and neurologist. Facial nerves can be preserved by monitoring the compound muscle action potential (CMAP) response. The differences in the amplitude and latency of CMAP are used as indicators during surgical interventions. However, baseline CMAPs cannot be recorded in the presence of large acoustic tumors. This paper presents a new way of estimating nerve function. Instead of a single CMAP examination, multi‐CMAP responses are obtained from a train of varied stimulus intensities and these are applied a mathematical model. Shifts in the mathematical model parameters reflect changes in facial nerve function. In this study, experiments conducted in frog revealed that shifts in the linear model parameters were related to the level of induced nerve injury. Significant differences in the slope parameter of the linear model were found between each nerve condition. The identification of healthy and severed nerves via a support vector machine (SVM) corresponded to 94% accuracy. This classification criterion could be used with surgical intervention to prevent severed facial nerve palsy in acoustic neuroma surgery. The proposed method could be used to estimate nerve outcomes without prior information of a CMAP baseline.

Lasting EEG/MEG Aftereffects of Rhythmic Transcranial Brain Stimulation: Level of Control Over Oscillatory Network Activity

A number of rhythmic protocols have emerged for non-invasive brain stimulation (NIBS) in humans, including transcranial alternating current stimulation (tACS), oscillatory transcranial direct current stimulation (otDCS), and repetitive (also called rhythmic) transcranial magnetic stimulation (rTMS). With these techniques, it is possible to match the frequency of the externally applied electromagnetic fields to the intrinsic frequency of oscillatory neural population activity (“frequency-tuning”). Mounting evidence suggests that by this means tACS, otDCS, and rTMS can entrain brain oscillations and promote associated functions in a frequency-specific manner, in particular during (i.e., online to) stimulation. Here, we focus instead on the changes in oscillatory brain activity that persist after the end of stimulation. Understanding such aftereffects in healthy participants is an important step for developing these techniques into potentially useful clinical tools for the treatment of specific patient groups. Reviewing the electrophysiological evidence in healthy participants, we find aftereffects on brain oscillations to be a common outcome following tACS/otDCS and rTMS. However, we did not find a consistent, predictable pattern of aftereffects across studies, which is in contrast to the relative homogeneity of reported online effects. This indicates that aftereffects are partially dissociated from online, frequency-specific (entrainment) effects during tACS/otDCS and rTMS. We outline possible accounts and future directions for a better understanding of the link between online entrainment and offline aftereffects, which will be key for developing more targeted interventions into oscillatory brain activity.