Effects of novelty, habituation, attention and distraction on the amplitude of the various components of the somatic evoked responses

Gating of the vertex somatosensory and auditory evoked potential P50 and the correlation to skin conductance orienting response in healthy men

A defect in auditory evoked potential (AEP) P50 gating supports the theory of information-processing deficits in schizophrenia. The relationship between gating of the mid-latency evoked potentials (EP) in the somatosensory and the auditory modalities has not been studied together before. In schizophrenia, we might expect the processing deficits to act on multiple modalities. We have examined the gating of median nerve somatosensory EP (SEP) following paired stimulation identical to the AEP P50 gating paradigm using interstimulus intervals (ISI) of 500, 750 and 1000 ms and the correlation of gating to the skin conductance orienting response (SCOR) in 20 healthy men. We measured mid-latency vertex components (SEP: P50, N65, P85 and N100; AEP: P30, N45, P50 and N80). The gating was most pronounced at ISI 500 ms where the SEP P50 and N100 gating were 0.59 and 0.37, respectively, as compared to a gating of 0.61 in P30, 0.33 in P50 and 0.45 in N80 in the AEP. Repetition effects in the two modalities were not correlated. AEP P50 gating was correlated to skin conductance level (SCL). The combination of recording repetition effects on the mid-latency EP in two modalities could provide a method for investigating if deficits of information processing in schizophrenia are cross-modal.

Subthalamic prelemniscal radiation stimulation for the treatment of Parkinson's disease: electrophysiological characterization of the area

Previous reports have provided evidence of a reticulo-thalamic system, extending from the mesencephalic reticular formation (MRF) to the ventrolateral thalamus (VL), involved in the production of tremor. In humans, a funnel of fibers in the posterior subthalamus named the prelemniscal radiations (Raprl) has been described as an exquisite target to treat tremor in cases of Parkinson's disease. In the present study, a group of 14 patients suffering from Parkinson's disease, with prominent unilateral tremor and rigidity, were implanted with tetrapolar depth brain stimulation (DBS) electrodes in Raprl to perform chronic electrical stimulation (ES) for the treatment of patient symptoms. Electrodes were left externalized to corroborate their placement throughout MRI studies and also to perform the following electrophysiological battery: (a) recording of somatosensory-evoked responses (SEP) through different electrode contacts and scalp by means of a paradigm to study the attention process; (b) evoking scalp EEG responses by stimulation with low (3 cps, 6 cps) and high (60-120 cps) frequencies with stimuli delivered through different electrode contacts, and (c) studying recovery cycle (RC) potentials in the Raprl while the upper MRF was being stimulated and, conversely, the RC in MRF while Raprl was being stimulated, before and after subacute Raprl stimulation. Thereafter, the electrodes were internalized and connected to a pulse generator (IPG) to carry on chronic ES, while the effects of stimulation were determined through a quantitative evaluation that measured phasic and tonic muscular activity with EMG recordings during different motor tasks. Results indicate the following: (a) that late, but not early, SEP components were recorded in Raprl and modulated in different attentive conditions; (b) that bilateral recruiting responses and spike and wave complexes were elicited by Raprl through low-frequency stimulation, while bilateral positive DC shifts induced by high-frequency stimulation were recorded, similar to those obtained in animals from MRF, and (c) that Raprl-ES induced RC inhibition at Raprl, but Raprl ES did not change MRF-RC. Long-term Raprl-ES induced a significant decrease in tremor and rigidity. It was concluded that Raprl represents a subthalamic circuit electrophysiologically related to MRF in the genesis of tremor and rigidity and in the process of selective attention. Raprl-ES induced a significant improvement in tremor and rigidity by causing inhibition of the stimulated area.

Attention and para-attentional processing. Event-related brain potentials as tests of a model

In 1972 when we began to analyze the vast amount of material from the laboratories of physiological psychologists, we had only a vague conceptualization of what a model of attention might look like. We began where everyone else had, with the view that everything had something to do with "arousal" but with Lacey's (1967) warning in mind that all of the dependent variables might not actually be measuring aspects of the same process. With this warning in mind, we were forced by the data to organize them into a three-systems mode. Since the first publication of this model in 1975, we have found increasing amounts of evidence to support and extend it. This evidence is briefly reviewed in the present paper in terms of the techniques employed in various types of investigation. Further, the current review of data has made it possible to specify the para-attentional substrate (the extrinsic lemniscal primary projection systems) upon which the three systems described in the earlier model operate. The earlier model was based on psychophysiological, neurobehavioral and neurochemical analyses while the current specification results from the results of recordings of event-related brain electrical responses. The conclusions derived from these results can be summarized as follows: First. It has become possible to distinguish controlled attention from the para-attentional pre- and post-attentive automatic processes upon which controls operate. Second. The pre- and post-attentive processes appear to be coordinate with activity in the extrinsic lemniscal primary sensory projection systems. Processing in these systems is reflected in the early components of event-related brain electrical potentials. These extrinsic systems are, however, not just throughputs for further processing. Rather, they are sensitive to the history of reinforcement which the subject has experienced. The concept of a limited channel capacity must, therefore, be modified to encompass this ability of organisms to improve, through practice, their competence to process a great deal of information in parallel. Competence, not capacity, limits central processing span. Third. A set of intrinsic extralemniscal processing systems has been identified to operate via a tecto-tegmental pathway to the reticular nucleus of the thalamus. The later components (N2P3, etc.) of event-related potentials have been shown to reflect processing in these systems and those that control them. Activity in these systems has been related to targeted conscious awareness.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatosensory event-related potentials following different stimulus conditions

We studied somatosensory event-related potentials (ERPs) in response to rare target, frequent nontarget and rare nontarget stimuli in 12 healthy subjects. Compared with the corresponding peaks following frequent stimuli, the responses elicited by rare target stimuli showed higher amplitudes for N70, P100 and N140 components and those evoked by rare nontarget stimuli showed higher amplitudes for N70 and N140 components. The P300 component following rare nontarget stimuli was shorter in latency and lower in amplitude than that elicited by target stimuli. ERP waveforms evoked by rare nontarget stimuli also showed obvious N240 and P300 components, which differed from those following frequent nontarget stimuli. These findings suggest that there are differences in signal processing in response to target, frequent nontarget and rare nontarget stimuli. The P300 component was distributed symmetrically and there was no significant hemispheric predominance with regard to any ERP component in response to either right or left side stimulation.

The effect of experimental muscle pain on the background electrical brain activity

The purpose of this project was to investigate whether specific effects in the background activity of the brain associated with the experience of pain can be depicted by means of quantitative electroencephalography (EEG). Lasting pain was induced by intramuscular infusion of hypertonic saline. The infusion was titrated to maintain pain for a sufficient time to obtain enough data for meaningful analysis. In a first study on 12 subjects, using a single, blind, repeated measures design with randomization of the administration of isotonic (0.9%) and hypertonic (5%) saline, and with subjects unaware of the fact that one substance was isotonic saline, a statistically significant pain response could be attributed to the administration of hypertonic saline. In a second study on 19 subjects, again using a randomized repeated measures design, topographic EEG measures were examined with respect to experimentally induced pain and pain from memory. Prior to each of these experimental stages, baseline recordings were obtained to satisfy the requirement of the crossover design. In addition to the common frequency bands used in EEG, we also obtained data in the frequency range of 35-100 Hz. The short-term variability of the selected EEG measures and their suitability as a sample estimate were assessed by computing the coefficient of variation from all selected epochs of a given subject at baseline. When compared to baseline, spectral analyzed EEG measures during experimental pain demonstrated statistically significant increases in the beta and 35-100 Hz frequency ranges, most notably at the temporal recording sites. There was no statistically significant difference between the EEG measures for (1) experimental pain vs. pain from memory, and (2) the 2 baseline recordings. The great variability in the topographical aspect of the between-subject response was interpreted as being strongly suggestive of the contamination of EEG measures by phenomena attributed to the jaw, facial and scalp musculature. In fact, Pearson correlation coefficients, as high as 0.92, were found between measures in the frequency band of 35-100 Hz and the beta frequency range. The unexplained variance in the heightened beta cortical power density can be attributed to the vigilance scanning of pain processes. Due to the fact that the statistically significant effect of pain on the topographic EEG measures were not different from imagined pain, we concluded that these effects are non-specific for pain.

Variation in evoked potential measures over the menstrual cycle: a pilot study

The P3 component of a visual event related potential (ERP) was studied for five consecutive weeks in six women with normal menstrual cycles. Serum concentrations of luteinizing hormone (LH), estradiol (E2) and progesterone were studied during the same period. Increases in P3 amplitude, although nonsignificant, were noted in the week preceding onset of menses. No significant changes in reaction times to target/nontarget stimuli were noted over the same time period.

Subcortical correlates of the somatic, auditory and visual vertex activities in man. I. Bipolar EEG responses and electrical stimulation

Bipolar responses correlated to somatic, auditory and visual vertex activities were studied in different subcortical structures of patients with implanted electrodes used as an electrophysiological procedure for surgical treatment. In addition, we studied the subjective responses of patients to electrical stimulation of subcortical structures where vertex-like activities (VA) were recorded, in order to determine their possible role in somatic, auditory and visual sensations. Typical subcortical VA evoked by somatic, auditory and visual stimuli, were recorded together from a single structure of a non-specific system including: reticulo-, medial dorsal-thalamic, orbito-frontal, limbic and striatal structures. Typical subcortical VA were formed by 4 consecutive components: O, A, B and C correlated to P1, N1, P2 and N2 of the surface VA. Polarity of component A was inverted between reticulo- and medial-thalamic structures while that of component B was inverted between medial thalamic and dorsal thalamic and between fronto-limbic and striatal structures. Typical subcortical VA were absent within specific thalamic nuclei and pathways in presence or absence of short latency responses evoked by specific sensory stimuli. Atypical subcortical VA of 1, 2 and 3 sensory modalities with inconsistent amplitudes, latencies and polarities were recorded from an intermediate zone surrounding and between specific and non-specific structures. Electrical stimulation of the non-specific structures at the reticulo- and medial thalamic levels elicited sensation of falling down and increase tension and tremor of the contralateral hand while no subjective responses were elicited by the stimulation at the dorsal thalamic, fronto-limbic and striatal levels. Stimulation of the specific structures and the intermediate zone elicited somatic, auditory and visual sensations with and without and apparent topographical organization, respectively.

Effect of fentanyl and naloxone on the P300 auditory potential

The effect of fentanyl (opioid agonist) and naloxone (morphine antagonist) on the amplitude, area and latency of the P300 auditory potential was studied in patients undergoing minor surgical procedures. Fentanyl (5.0 micrograms/kg), naloxone (3.0 micrograms/kg) and isotonic saline (for control) were injected intravenously through a catheter just before surgery, and following a single-blind procedure and three different pharmacological paradigms with three consecutive conditions each: (1) initial baseline (C), saline (S) and late baseline (C'); (2) C, fentanyl (F) and C'; (3) C, naloxone (N) and C'. Fentanyl significantly reduced the amplitude and area with no changes in the latency of small (S) and large (L) P300 potentials. Concomitantly, fentanyl increased the number of omitted counts of the target tones of the "odd ball" P300 test and the spatial threshold of the two point discrimination test in patients with small and large P300 potentials. Naloxone significantly increased the amplitude and area and decreased the latency of the small P300 potential and decreased the amplitude and area with no changes in latency of the large P300 potentials. Concomitantly, naloxone decreased the number of omitted counts of the patients with small but not large P300 potentials and decreased the spatial threshold in patients with both small and large P300 potentials. Neither fentanyl nor naloxone produced systematic changes in the evaluation of pain and hearing of patients with small and large P300 potentials. Although dramatic changes in pulse, blood pressure, respiration and EEG were found in some cases immediately after the administration of fentanyl and naloxone, these changes were not consistent and were not present at the time other tests were performed.

Effect of fentanyl and naloxone on human somatic and auditory-evoked potential components

The effect of fentanyl (a morphine agonist) and naloxone (a morphine antagonist) on early and late components of somatic (SEP)- and auditory (AEP)-evoked potentials was studied in patients undergoing minor surgical procedures, in which these compounds were used in producing and regulating a state of neuroleptanalgesia. Fentanyl (2.5, 5.0 and 10.0 micrograms/kg), naloxone (1.5 and 3.0 micrograms/kg) and isotonic saline (for comparative purposes) were injected just before surgery, intravenously through a catheter and following a single blind procedure and three different pharmacological paradigms with four consecutive conditions each: (1) Initial baseline (C), first saline (S), second saline (S') and late baseline (C'). (2) C, First fentanyl (F), second naloxone (N') and C. (3) C, First naloxone (N), second fentanyl (F') and C'. Special care was taken in controlling the constancy of the muscular and cochlear receptor activation concomitant to somatic-evoked potentials and auditory-evoked potentials, determined by the amplitude of the muscular response at the tenar muscles (MP) and component I of the brain stem potentials ( ABSP ). Evaluation by the patients pain, topognoses and hearing and other somatic and autonomic indicators of the level of the analgesic response were also controlled. Fentanyl significantly reduced, while naloxone increased, the amplitude of late components P150 of somatic-evoked potentials and auditory-evoked potentials. Concomitantly, fentanyl increased, while naloxone decreased, the spatial threshold (two point discrimination test) at finger tip and arm. These effects were observed in patients taking various doses, although they were more consistent with larger doses of these compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Wakefulness-sleep modulation of thalamic multiple unit activity and EEG in man

Quantitative changes in the number of EEG waves and MUA neuronal spikes of various thalamic nuclear groups were studied during steady and transitional wakefulness-sleep states in a group of patients with implanted electrodes, used as an electrophysiological procedure for the surgical treatment of unilateral tremor and rigidity. Thalamic nuclei included ventroposterolateral (VPL), ventrolateral (VL) and centromedian (CM). Steady states included initial wakefulness (W1), slow wave sleep (SWS) I, II, IV and IIL, paradoxical sleep phasic (PSP) and tonic (PST) and final wakefulness (W2). Transitional states included transition from SWS to PSP (transition) and from sleep to W2 (arousal). (1) There was a significant correlation in EEG and MUA between different thalamic nuclei simultaneously recorded in the same patient during different steady-states. (2) Thalamic MUA significantly decreased from W to SWS, increased from SWS to PS and SWS to W2, while thalamic EEG significantly decreased from W to SWS, increased from SWS to W2 but was not significantly modified from SWS to PS, consecutive steady-state shifts. (3) Thalamic MUA significantly decreased while EEG remained unchanged from PSP to PST consecutive steady-state shifts. (4) Both thalamic MUA and EEG significantly decreased from SWS II to IIL while they were not systematically modified from W1 to W2 indirect steady-state shifts. (5) Thalamic MUA significantly increased 1 sec before transition and arousal while EEG increased 5 sec after arousal and did not change during transition.

A peculiar rhythmic EEG activity from ventrobasal thalamus during paradoxical sleep in man

A peculiar 3/sec rhythmic EEG activity (named Vc rhythm) was consistently found at the ventrobasal thalamus (nucleus ventrocaudalis) during paradoxical sleep of patients with implanted electrodes used as an electrophysiological procedure for identification of the thalamic targets for the surgical treatment of tremor and rigidity. The Vc rhythm was formed by high voltage, sharp biphasic positive negative potentials which were absent during wakefulness, rare and isolated during slow wave sleep, increased in number and organized in trains during paradoxical sleep and blocked during arousal. Significant changes in number of Vc waves were found when patients shifted through these wakefulness-sleep states. Integrated EMG multiple unit activity also showed significant changes during these wakefulness-sleep shifts, which were parallel although inverse to those showed by Vc waves. A significant negative correlation (r = -0.7126) between number of Vc waves and EMG units was found. In contrast, Vc waves showed no correlation with other electrophysiological indicators of thalamic excitability (multiple unit activity and early evoked potentials) and sleep (scalp EEG frequency and ocular movements).

Differential effect of task relevance on early and late components of cortical and subcortical somatic evoked potentials in man

The effect of "task relevance" on early and late components of cortical and subcortical somatic evoked potentials (SEPs) was studied in a group of Parkinsonian patients operated on under local anesthesia for treatment of prominent unilateral tremor. 1. SEPs produced by median nerve stimulation were found at contralateral cortical (ss), thalamic (vcpci, vcai), lemniscal (Lm), postilemniscal (PoLm), prelemniscal (Raprl) and reticular (Ttc) regions. No SEPs were found in other contiguous thalamic (M,Pf, ce) and subthalamic (Q) regions. 2. Subcortical early SEP components consisted of two monophasic positive potentials distributed within a circumscribed thalamo-lemniscal region where electrical stimulation elicited consistent sensory responses circumscribed to contralateral hand and face. In contrast, subcortical late SEP components consisted of monophasic or polyphasic, positive or negative potentials distributed in a widespread, thalamic, lemniscal, prelemniscal and reticular region where elecrical stimulation elecited sensory or motor responses of various types. Subcortical early and late SEP components appeared together in lemniscal, thalamic and cortical regions but they wers separated at postlemniscal (only early) and prelemniscal and reticular ones (only late). 3. Significant amplitude changes in cortical and subcortical late SEP componets were found concomitant to variations in "task relevance": they decreased when patients shifted from novelty to habituation, they increased when patients shifted from habituation to attention and they decreased when patients shifted from attention to distraction. In contrast, no significant ampiltude changes in cortical and subcortical early components were found when patients shifted through these various "task relevance" conditions.

Differential effect of thalamic and subthalamic lesions on early and late components of the somatic evoked potentials in man

The effect of thalamic (Vo), subthalamic (Raprl) and combined (Vo-Raprl) unilateral lesions on early and late components of the somatic evoked potentials (SEPs) was investigated in a group of 16 cases operated on for the treatment of contralateral dyskinetic movements. In these cases, SEPs were independently produced by stimulation of the left and right median nerves and recorded at the corresponding somatosensory scalp regions. In addition, EEG frequencies and reaction time (RT) were independently and bilaterally determined. These tests were performed before and after operation and changes in SEP, EEG and RT were quantitatively evaluated in relation to both ipsilateral preoperative and contralateral postoperative controls. 1. All cases with either thalamic or combined lesions involving Vo nucleus showed an ipsilateral reduction in amplitude of late SEP components and EEG frequency and a contralateral increase RT. A peculiar form of "inattention" to the contralateral hand was also found. Quantitative evaluation of the total group showed significant amplitude reduction in late SEP components in relation to both ipsilateral preoperative and contralateral postoperative controls. Changes in EEG and RT were only significant in relation to their preoperative ipsilateral controls. 2. Two cases with subthalamic lesions and quick postoperative recovery showed no apparent change in SEP, EEG and RT. Three cases with similar lesions and slow postoperative recovery showed bilateral decrease in amplitude of late SEP components, EEG frequency and increase in RT. Clinical inattention to contralateral hand was also found in all these cases. Quantitative evaluation of the total group showed no significant changes in these parameters in relation to preoperative controls. 3. None of these lesions produced changes in early SEP components or somatosensory deficits at the contralateral hand.

Selective attention and evoked potentials in humans--a critical review

Human evoked-potential research on the neurophysiological substrate of selective attention is reviewed. Most of these studies report enhanced amplitudes of potentials evoked by attended (task-relevant, meaningful, important, etc.) stimuli the results of which are generally regarded as providing an electrophysiological correlate for selective attention. In accepting such claims, there appears to be two major procedural problems generally not satisfactorily solved in these studies: (1) the inability to reliably separate the specific and non-specific physiological changes concomitant with selective attention from each other; and (2) inadequacy of peripheral sensory control possibly inducing contaminating changes already at the level of the proximal stimulus. Problem (1) originates from, and the importance of (2) is emphasized by, the temporal stimulus structure of experimental tasks in these studies which allows the subject to predict above the chance level the relevant events and, thus, to differentially prepare himself for these in advance (increased non-specific arousal and selective peripheral sensory orientation, the latter often made possible by insufficient control, have possibly been among these changes). Those studies to which these two (and other) remarks do not apply at all or only to an insignificant degree have generally shown no selective evoked-potential changes (or these changes have occurred only with a long latency ('P3' or 'P300') making their interpretation especially uncertain). There is one exception for this general notion, the reasons for and significance of which are dealt with in detail. Finally, the difficulties and inherent limitations of inferring brain events from scalp-recorded evoked-potential data, especially with respect to the important selective-filter hypothesis of selective attention, are extensively discussed and, in the light of these difficulties, some trends for future research proposed.

Evoked potential correlates of selective attention with multi-channel auditory inputs

Ten subjects were presented with a random sequence of 50 msec tone pips at a rapid rate (averaging one tone every 225 msec). The tones came from four different sound sources or sensory "channels" each having a different pitch (2000,4000,1000, and 500 c/sec respectively) and perceived spatial position (spaced equidistant across the head). Within each sensory "channel" a random 10% of the tones were of a slightly higher pitch (designated as "targets"). The subject attended to one channel at a time for 7.5 min and counted the targets in that channel. The auditory evoked vertex potential elicited by a channel of stimuli when attended was compared with the mean vertex potential elicited by those same stimuli when the other three channels were being attended. The N1 component (latency 80130 msec) measured re a baseline revealed an increase with attention (82% in the baselineN1 measure, P less than 10-). It was concluded that: (1) this N1 enhancement could not be attributed to peripheral mechanisms acting on sensory transmission; (2) this N1 enhancement reflects a "finely tuned" selective attention to one channel of stimuli among several concurrent and competing channels; and (3) a probable relationship exists between the information load on the subject and the magnitude of this EP enhancement with selective attention.

Somatic evoked response components and recovery functions in subjects with mu and alpha rhythms

Subjects with prominent rolandic mu and alpha rhythms showed similar late somatic evoked response (SER) components but different SER recovery functions. A late P5x component was present when SER were superimposed on mu and alpha rhythms spontaneously recorded from the rolandic region of inattentive individuals. Since P5x was not present in other inattentive subjects unless SER were superimposed on a rhythmic rolandic activity evoked by an attentive situation, it seems reasonable to assume that the P5x component is partially due to spontaneous or evoked rolandic EEG rhythmicity. In addition, single propioceptive stimuli produced blocking of mu rhythm and a flat recovery function of the P5a component. In contrast, similar stimuli produced an enhancement of alpha rhythm and a periodic amplitude modulation curve of the P5a component. These results suggest that the P5a component is mediated by the same neurophysiological mechanisms which block or modulate the spontaneous rolandic EEG rhythms.