Neurobehavioral aspects of brain slow potentials

Voluntary movements and event-related potentials in Parkinsonians (stages 1-2)

The temporal analysis of goal-directed movements has revealed that the delay of movement initiation in Parkinsonians might be decreased or abolished by altering the preparatory set and increasing the motivation level of patients. Averaged event-related potentials (ERPs) during different psychomotor reactions to light stimuli, ignore condition and difference waves between attend (reactions) and ignore conditions were analyzed in 19 Parkinsonian patients (stages 1-2) and 12 healthy subjects. A deceleration of psychomotor reactions in the patients was found to be accompanied by a decrease in ERPs, especially in frontal recording. This decrease was affected by an altered pre-stimulus preparatory set in the patients. The decrease of endogenous ERPs (difference waves) was associated to a greater extent with the motor acts than with cognitive operations. The deceleration of the voluntary movements in Parkinsonism is assumed to be connected with 'deficit' of the frontal activation due to a dysfunction of the basal ganglia.

Sensory-evoked potentials as indices of neurotoxicity in the rat: effect of 4-tert-butyltoluene

The use of evoked potentials to measure neurotoxicity was evaluated using 4-tert-butyltoluene (TBT) as a test compound. Male Wistar rats were habituated to the recordings of auditory- and flash-evoked potentials until the combined waveform of the evoked potentials reached a steady state. The rats were then divided into three groups and exposed to 0, 50 and 150 ppm TBT for 6 h, and the auditory- and flash-evoked potentials were measured for up to 288 h after exposure. Event-related potentials specifically associated with the temporal pairing of auditory and visual stimuli were not apparent in the recordings. The peak-to-peak values of selected components, integrated amplitude and power spectra of the waveforms in exposed rats were significantly different from control values for at least 288 h in the group exposed to 150 ppm TBT and for 120 h in the group exposed to 50 ppm TBT. It is concluded that evoked potentials may be used for detection and characterization of minor neurofunctional changes due to low-dose exposure to chemicals.

Preliminary study on subcortical slow potentials related to the readiness potential in monkey

Two female rhesus monkeys with cortical and subcortical DC-electrodes were studied during self-paced operant responding to determine the feasibility of mapping the intracerebral distribution of readiness potentials (RP). These potentials reflect preparatory aspects of motor activation and may be useful indicators of subcortical areas involved in preparatory set. The monkeys had learned to execute the task appropriately after 17 and 28 sessions respectively; one monkey's performance was very stable, and the other's erratic. However, relatively comparable RPs were recorded from the monkeys when recordings from sessions involving good performance were considered. RPs of relatively large amplitude appeared in electrodes positioned near the substantia nigra and pretectal/collicular region; smaller responses were observed in cortex and midbrain reticulum and, in one monkey, the caudate nucleus. These findings indicate the feasibility of such studies and suggest that, like the contingent negative variation, RPs occur in many subcortical regions.

Inhibitory influence of oxytocin infusion on contingent negative variation and some memory tasks in normal men

A double-blind study combining electrophysiological and psychometrical approaches was carried out to investigate the central effects of an intravenous oxytocin (OT) infusion in normal men. Contingent negative variation (CNV) was selected as the measure of central cognitive evoked potential, and the psychometric tests measured mood, vigilance and memory. OT infusion induced a significant decrease of CNV amplitude and an increase of post-imperative positive potentials in vertex derivations. A similar effect was still evidenced one week after treatment in frontal derivations, suggesting a long time effect of OT on human brain. No significant influence of OT on mood or vigilance tests was apparent; only one item of a memory test revealed a significant impairment of some mnesic performances. These observations provide new electrophysiological arguments supporting a central action of peripheral OT administration in man.

The generation of cortical slow potentials in the rat anaesthetised with urethane and their modification by nicotine

This paper reports the generation of cortical slow potentials (SP), similar to the human contingent negative variation, in rats anaesthetised with urethane. Rats previously implanted with silver/silver chloride electrodes for recording slow potentials from the frontal cortex were anaesthetised with urethane, and given extensive associative conditioning in which a 100 msec, 70 dB tone (S1) preceded electric tail shock (S2). The S1-S2 interval was initially set at 0.5 sec, and increased over a number of training sessions to 3 sec. Negative slow potential responses developed during the interval between S1 and S2. Once the slow potential response was fully developed, it persisted without habituation during subsequent sessions. Withholding tail shock (S2) resulted in a rapid extinction of the slow potential response to S1 alone. In further experiments, rats (n = 8) that generated steady slow potentials under urethane, were injected with saline (n = 4) or nicotine (0.4 mg/kg, s.c.; n = 4), and their responses measured 0-10, 15-25 and 30-40 min after administration. While saline did not affect the magnitude of the slow potential responses compared with pre-saline control values, nicotine (0.4 mg/kg) caused significant decreases in the magnitude of slow potentials during all the measurement intervals. These results demonstrate that cortical slow potentials can be generated in rats anaesthetised with urethane, and that these slow potentials are sensitive to drugs such as nicotine. The slow potential responses measured in the rat anaesthetised with urethane thus have similar characteristics to those generated in the conscious rat. Such a preparation may therefore prove useful in carrying out experiments on slow potentials that were previously difficult or impossible in conscious animals.

Single-unit and slow potential responses from rat frontal cortex during associative conditioning

Single-unit and slow potential responses were recorded from the frontal cortex of unanesthetized, restrained rats trained to associate an auditory cue (tone) with rewarding medial forebrain bundle stimulation. Slow potential responses to the unpaired tone were minimal whereas large negative slow potential responses developed to the paired tone. Units were selected which had large-amplitude action potentials and positive first deflections, characteristics suggesting that the recordings were derived from pyramidal neurons. Responses of excitation, inhibition, and no change were observed during tone presentation. Forty-five percent of the units responded to the unpaired tone; with pairing, 90% of the units demonstrated significant responses. Furthermore, the magnitude of the excitatory responses was enhanced by pairing and a distribution pattern developed in which the overall response of the more superficial units was activation whereas deeper units were inhibited. The results suggest that the conditioning-related negative slow potential responses recorded from the surface of the rat frontal cortex reflect excitatory processes which are associated with an enhanced firing rate of neurons in the upper layers.