Evoked Potentials: How? What? and Why?

Glass pipette-carbon fiber microelectrodes for evoked potential recordings

Current methods for recording field potentials with tungsten electrodes make it virtually impossible to use the same recording electrode also as a lesioning electrode, for example for histological confirmation of the recorded site, because the lesioning procedure usually wears off the tungsten tip. Therefore, the electrode would have to be replaced after each lesioning procedure, which is a very high cost solution to the problem. We present here a low cost, easy to make, high quality glass pipette-carbon fiber microelectrode that shows resistive, signal/noise and electrochemical coupling advantages over tungsten electrodes. Also, currently used carbon fiber microelectrodes often show problems with electrical continuity, especially regarding electrochemical applications using a carbon-powder/resin mixture, with consequent low performance, besides the inconvenience of handling such a mixture. We propose here a new method for manufacturing glass pipette-carbon fiber microelectrodes with several advantages when recording intracerebral field potentials.

Auditory-evoked response morphology in profoundly-involved multi-handicapped children: comparisons with normal infants and children

The developmental and difference/defect theories have been used to explain auditory development in some multi-handicapped children. If developmental factors influence auditory response behaviors, it might be predicted that evoked potentials measured from the central auditory nervous system would reflect similar developmental influences in multi-handicapped children. The purpose of this study was to compare auditory-evoked-potential waveform morphology between profoundly-involved multi-handicapped children and normal infants and children. Auditory brainstem response (ABR) and middle-latency response (MLR) morphology were examined from waveform descriptions, wave detection, latency, amplitude, and spectral energy measures. The majority of handicapped subjects exhibited response morphology unlike that of normal children or infants. ABR/MLR morphology for handicapped children was characterized by depressed responses and substantial waveform variability. The results of this study tended to support the difference/defect theory.

Response properties of long-latency event-related potentials evoked during NREM sleep

The experiments reported here sought to investigate whether the K-complex evoked during sleep is comprised of activity from two separate physiological systems with different response properties. To that end, the parameters of stimulation in a two tone auditory 'odd-ball' task were varied systematically as stimuli were presented to subjects during NREM sleep. During experiment 1, the frequency (pitch) of the odd-ball stimulus varied systematically while intensity (loudness) was matched between tones. During experiment 2, pitch was matched between tones while the loudness of the odd-ball stimulus was varied. The long-latency event-related potentials (ERPs) N2 and P3 could be dissociated from the K-complex (N3 and P4) in response to these parametric manipulations. Information processing occurs during sleep, and is reflected in ERPs with a morphology largely analogous to those observed under similar conditions while subjects are awake. The second (K-complex) system is sleep specific. A model was constructed to explain the activity of these two hypothesized systems. As predicted by the model, K-complex latency was longer in Stage 2 when N2 and P3 were also active, than in Stage 4 where N2-P3 activity was lessened. These results support the two-system hypothesis; electrical brain activity evoked during sleep should not be considered a unitary sleep-specific response. Furthermore, the data indicate that the K-complex is sensitive to the physical characteristics of stimuli, that the sleeping brain processes information to a high degree, and that the 'endogenous' components of the ERP observed in awake humans reflect more automatic processes than previously suspected.

Effect of intertrial intervals on recovery and amplitude of electrodermal reactions

Convincing findings have been published about the importance of prior activity on electrodermal recovery. However, these studies mainly used tone tasks as an experimental paradigm. The present research investigated the influence of prior activity by changing the intertrial intervals (ITI) in cognitive and reaction time tasks. Results indicated that ITI had no effect on amplitude but had a significant effect on recovery time, a longer ITI period producing a longer recovery curve. No correlation was found between recovery and amplitude. Analysis also indicated that variable intervals should not be recommended between the tasks. These observations emphasize the importance of prior activity on electrodermal recovery in more complex tasks.

Auditory brainstem evoked potentials in evaluating the efficacy of surgical ventilation of the middle ear

Conductive hearing loss in children is most commonly associated with Secretory otitis media (S.O.M.). Since auditory brainstem evoked potentials (ABEP) reflect conductive damage in prolonged peak latencies, the present study evaluated the efficacy of surgery for ventilating the middle ear, by comparing changes in peak latencies. These changes were compared in 4 groups of children (4-12 years old): children with S.O.M. in the past, who recovered as a result of conservative treatment; children with S.O.M. in the past, who had been operated on with insertion of ventilation tubes (V.T.); children with S.O.M. in the past, who had been operated on and who still had V.T. at the time of study, and a control group with healthy ears. In all, 183 ears were tested. The results indicate that there is no significant audiometric and electrophysiological difference between the groups who recovered with or without V.T.

Force uncertainty of voluntary movement and human movement-related potentials

Five movement related potentials, the Bereitschaftspotential (BP), the pre-motion positivity (PMP), the motor potential (MP), the first negative potential during the movement (N1) and the late positive component (LPC) were recorded from human subjects performing right index finger flexions under conditions when the resistive forces (70 N/cm or 10 N/cm) were predictable and when they were unpredictable. The BP was larger prior to the larger force in the certain condition. In the uncertain condition, the BP was similar to that associated with the larger force in the certain condition suggesting that the subjects tended to prepare for the heavy resistance when confronted with force uncertainty. The MP revealed enhanced negativity over the left parietal cortex when the force was unpredictable. The N1 was significantly larger during the high force movement, especially in the uncertain condition. The results support the view that pre-movement compensation for force unpredictability does exist as reflected by the MP over the parietal areas.

Moving sound sources: techniques and applications

A stimulating device for the application of moving acoustic signals of varying form and velocity is described. The apparatus functions on the principle of intensity stereophony and permits continuous smooth sound movements in a vast range of different forms and frequencies. Furthermore, simultaneous application of vestibular and optokinetic stimuli is possible. Cortically evoked potentials, voluntary and involuntary eye movements, and influences upon body sway from moving acoustic signals are offered as examples for applicability.

Risk-taking and the human bereitschaftspotential

The effects of response probability and feedback predictability on the human Bereitschaftspotential (BP) were examined in a probability-matching paradigm. The subjects were to guess, by pressing one of two buttons, which of two possible feedback lights could be lighted. The a priori probabilities (30%-70%) of the feedback were known to the subjects. This task was performed both when the feedback was unpredictable and when it was perfectly predictable from the prior information. The BP was enhanced only when the subjects guessed the improbable feedback when it was unpredictable, thereby putting themselves 'at risk.' This effect seemed to be independent of any concurrent contingent negative variation. The results indicate that the BP is sensitive to trial-by-trial variation of the psychological state, which is in some way related to intention.