Browsing by Author "J. Basser, Peter"
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Item Measuring conduction velocity distributions in peripheral nerves using neurophysiological techniques(2020) Ni, Zhen; Vial Undurraga, Felipe; V. Avram, Alexandru; Leodori, Giorgio; Pajevic, Sinisa; J. Basser, Peter; Hallett, MarkObjective: To determine how long it takes for neural impulses to travel along peripheral nerve fibers in living humans. Methods: A collision test was performed to measure the conduction velocity distribution of the ulnar nerve. Two stimuli at the distal and proximal sites were used to produce the collision. Compound muscle or nerve action potentials were recorded to perform the measurements on the motor or mixed nerve, respectively. Interstimulus interval was set at 1–5 ms. A quadri-pulse technique was used to measure the refractory period and calibrate the conduction time. Results: Compound muscle action potential produced by the proximal stimulation started to emerge at the interstimulus interval of about 1.5 ms and increased with the increment in interstimulus interval. Two groups of motor nerve fibers with different conduction velocities were identified. The mixed nerve showed a wider conduction velocity distribution with identification of more subgroups of nerve fibers than the motor nerve. Conclusions: The conduction velocity distributions in high resolution on a peripheral motor and mixed nerve are different and this can be measured with the collision test. Significance: We provided ground truth data to verify the neuroimaging pipelines for the measurements of latency connectome in the peripheral nervous system.Item Measuring latency distribution of transcallosal fibers using transcranial magnetic stimulation(2020) Ni, Zhen; Leodori, Giorgio; Vial Undurraga, Felipe; Zhang, Yong; V. Avram, Alexandru; Pajevic, Sinisa; J. Basser, Peter; Hallett, MarkBackground: Neuroimaging technology is being developed to enable non-invasive mapping of the latency distribution of cortical projection pathways in white matter, and correlative clinical neurophysiological techniques would be valuable for mutual verification. Interhemispheric interaction through the corpus callosum can be measured with interhemispheric facilitation and inhibition using transcranial magnetic stimulation. Objective: To develop a method for determining the latency distribution of the transcallosal fibers with transcranial magnetic stimulation. Methods: We measured the precise time courses of interhemispheric facilitation and inhibition with a conditioning-test paired-pulse magnetic stimulation paradigm. The conditioning stimulus was applied to the right primary motor cortex and the test stimulus was applied to the left primary motor cortex. The interstimulus interval was set at 0.1 ms resolution. The proportions of transcallosal fibers with different conduction velocities were calculated by measuring the changes in magnitudes of interhemispheric facilitation and inhibition with interstimulus interval. Results: Both interhemispheric facilitation and inhibition increased with increment in interstimulus interval. The magnitude of interhemispheric facilitation was correlated with that of interhemispheric inhibition. The latency distribution of transcallosal fibers measured with interhemispheric facilitation was also correlated with that measured with interhemispheric inhibition. Conclusions: The data can be interpreted as latency distribution of transcallosal fibers. Interhemispheric interaction measured with transcranial magnetic stimulation is a promising technique to determine the latency distribution of the transcallosal fibers. Similar techniques could be developed for other cortical pathways.