Electrical Stimulation Of Digital Nerves Research Articles

Prepulse inhibition of the blink reflex by laser stimuli in normal humans

The subcortical integrative effects of laser-induced activation of pain ascending tracts were examined in 11 healthy volunteers, aged 22–52 years. Subjects underwent either CO 2 laser stimulation at the dorsum of the hand, electrical stimulation of digital nerves at the 3rd finger, or mechanical taps to the first dorsal interosseous space, preceding a blink reflex elicited by a supraorbital nerve electrical stimulus. The percentage inhibition induced in the R2 response of the blink reflex was similar for the three different stimulus modalities, but occurred at a different time interval. Compared to control trials, the R2 response of the test trials was a mean of 23.1% at the interval of 250 ms with laser stimuli, 17.4% at the interval of 100 ms with electrical stimuli to the 3rd finger, and 20.6% at the interval of 90 ms with a mechanical tap to the 1st interosseous space. Activation of pain receptors induces prepulse inhibition of the blink reflex at a delay corresponding to a slowly conducting pathway. The percentage inhibition is similar to that observed with other somatosensory inputs.

Interfering cutaneous stimulation and the muscle afferent contribution tocortical potentials

Cerebral potentials were recorded in response to selective stimulation using microelectrodes of muscle afferents in motor fascicles innervating the intrinsic muscles of the foot or at the motor point of abductor hallucis. The early components of these potentials (P40, N50 and P60) were consistently attenuated by continuous tactile stimulation of related skin areas and by electrical stimulation of digital nerves, timed so that the digital volley reached cortex approximately 5 msec before the muscle afferent volley. The same conditioning cutaneous inputs also attenuated the cerebral potentials evoked by selective stimulation of cutaneous afferents. These findings confirm that there are intermodality and intramodality interactions between low-threshold cutaneous and muscle afferents and between cutaneous afferents, respectively. The findings indicate that ‘interference phenomena’ (Kakigi and Jones 1986) can occur between different afferent modalities, and within any one modality, and cannot be used to determine the afferent species responsible for the test evoked potential.

Modulation of reflex and voluntary EMG activity in wrist flexors by stimulation of digital nerves in hemiplegic humans

Changes in EMG activity in the wrist flexor muscles were studied in response to electrical stimulation of digital nerves and to sudden extension perturbations at the wrist produced by a torque motor in human subjects with unilateral cerebral hemisphere lesions. With the subjects maintaining a steady voluntary contraction against a constant load, digital nerve stimulation produced a series of excitatory and inhibitory changes in tonic EMG activity from the wrist flexors in both the normal and paretic arm. The most consistent response was a period of EMG inhibition beginning approximately 38 msec after the stimulus and lasting approximately 35 msec. With relatively weak electrical stimuli, there was less EMG inhibition in the paretic arm than in the normal arm; with stronger stimuli, the inhibitory response was similar in the two arms. The electrical stimuli and mechanical perturbations were then delivered together, with the interval between them adjusted so that the expected period of inhibition following electrical stimulation coincided with either the early (M1) or the long latency (M2) components of the stretch reflex. In the normal arm electrical stimulation produced more inhibition of the M2 component than of the M1 component. In the paretic arm, inhibition during the M2 component was less marked and similar in degree to that which occurred during M1. These results are compatible with the view that M1 and M2 are normally mediated by separate neural pathways. The long latency EMG activity evoked by muscle stretch in the paretic arm of hemiplegic patients may be generated by pathways or mechanisms different from those in the intact arm.

Effect of cutaneous nerve stimulation on voluntary and stretch reflex electromyographic activity in wrist flexors in humans.

1. Changes in electromyographic (e.m.g.) activity in the wrist flexors of normal human subjects were studied in response to electrical stimulation of digital nerves and to sudden extension perturbations at the wrist produced by a torque motor. 2. With the subjects maintaining a steady voluntary contraction, stimulation of the digital nerves produced a series of excitatory and inhibitory changes in the tonic e.m.g. activity from the wrist flexors. The most prominent and consistent response was a period of e.m.g. inhibition beginning 39 ms after the stimulus and lasting for approximately 36 ms. 3. The stretch reflex evoked by extension perturbations of the wrist consisted of an early response (M1) with an onset latency of approximately 30 ms, and a late response (M2) with an onset latency of approximately 60 ms. 4. The electrical stimuli and the mechanical perturbations were then delivered together, varying the interval between them so that the period of inhibition resulting from the electrical stimuli occurred at the same time as the M1 or M2 components of the stretch reflex, or during the later voluntary response. 5. The amount of e.m.g. inhibition during the M2 component was significantly greater than that during M1 (P less than 0.02). This result is compatible with the view that M1 and M2 are mediated by separate neural pathways.