A.J.W. Boelhouwer

Optimal EMG signal bandwidth and interelectrode distance for the recording of acoustic, electrocutaneous, and photic blink reflexes

The bandwidth for the recording of the orbicularis oculi blink reflex electromyogram (EMG) response is optimal when low-frequency artifacts, such as motion artifacts and cross-talk from other muscles, are maximally suppressed, whereas true EMG signal power is maximally retained. The optimal bandwidth was investigated for acoustic, electrocutaneous, and photic blink reflexes. Reflexes were recorded with varying bandwidth and interelectrode distances of 12 and 36 mm. Power spectra of the EMG signals were calculated and compared with a theoretical spectrum of the uncontaminated EMG signal. For both electrode distances, the optimal bandwidth was on the average 28-500 Hz for acoustic and electrocutaneous blink reflexes and 12-500 Hz for photic blinks. Using photic stimuli, however, a high-pass filter frequency larger than 12 Hz (probably at least 30 Hz) in combination with occlusion of the eye will be necessary to avoid influences of retinal potentials. Given the optimal bandwidth, a larger electrode spacing may be expected to moderately improve the detectability of small blinks in all stimulus conditions.

The effect of acoustic pulse intensity upon the electrically elicited blink reflex at positive and negative stimulus onset asynchronies

The present study examined the effects of acoustic pulse intensity and stimulus onset asynchrony (SOA) on the electrically elicited startle reflex response. Subjects were presented with 165 startle eliciting stimuli: 15 control trials with no acoustic pulse, and 5 trials at each pulse intensity (50, 70, and 90 dB) for each SOA (-80, 60, -40, -20, 0, 20, 40, 60, 80, and 100 ms). The results demonstrated R2 magnitude facilitation at negative, simultaneous, and short positive SOAs. R2 facilitation was greatest in the 90 dB condition and least in the 50 dB condition. R1 facilitation at short positive SOAs was greater for more intense acoustic pulses. These data support the notion that R2 facilitation at near-zero SOAs may be the result of combination of pulse induced potentiation of the electrically elicited startle response and temporal summation of the effects of electrical and acoustic stimuli at the facial motor nucleus.

Blink reflexes and preparation

Blink reflexes were evoked during a foreperiod of 3 sec between a warning signal (WS) and a reaction signal (RS). In a between group design, two possible reactions following RS were investigated: 20 subjects always reacted with both hands, another group of 20 subjects always reacted with a voluntary blink. A manual response was assumed not to involve the circuit of the blink reflex, whereas a blink as a response was thought to be (at least partly) realized via the same circuit as the blink reflex. Both groups showed a strong increase of the early component (R1) of the blink reflex during the first 300 msec after WS, while the late polysynaptic component (R2) showed a strong inhibition during the same period. R1 did not decrease as a function of presentation order when the demanded reaction was a voluntary blink. No other inhibition or excitation related to the type of reaction after RS was observed during the foreperiod before RS.