Nancy K. Squires

Anatomical and Physiological Substrates of Event‐Related Potentials: Two Case Studies

Because an excellent tutorial introduction to the anatomical and physiological substrates of event-related potentials (ERPs) is available (Goff et al.. 1978), our objective in this chapter is not a general tutorial review. Rather, we intend to consider in detail the anatomical and physiological substrates of two classes or families of ERPs that have been the subject of intense investigation in recent years: (a) the auditory “ N I P ~ complex” and (b) P300 and related “endogenous” potentials. Our hope is that such a “case study” approach to ERP substrates will not only provide the reader with a thorough review of recent research findings, but will also provide a critical analysis of both the theoretical and empirical foundations of inferences about the neural substrates of ERPs. Our consideration of each family of potentials will consist of (a) a brief descriptive introduction, including the identifying characteristics of the potentials under consideration and the experimental conditions under which they can be obtained; (b) a detailed consideration of the different types of evidence that have been used to formulate and

Brainstem auditory evoked responses in man. I. Effect of stimulus rise–fall time and duration

Short latency (under 10 msec) evoked responses elicited by bursts of white noise were recorded from the scalp of human subjects. Response alterations produced by changes in the noise‐burst duration (on time), interburst interval (off time), and onset and offset shapes are reported and evaluated. The latency of the most prominent response component, wave V, was markedly delayed with increases in stimulus rise time but was unaffected by changes in fall time. Increase in stimulus duration and therefore loudness resulted in a systematic increse in latency, probably due to response recovery processes, as this effect was eliminated with increases in stimulus off time. The amplitude of wave V was insensitive to changes in signal rise and fall times, while increasing signal on time produced smaller amplitude responses only for sufficiently short off times. It is concluded that wave V of the human auditory brainstem‐evoked response is solely an onset response.Subject Classification :[43]65.59.[43].65.75.

10 Human Endogenous Limbic Potentials: Cross-Modality and Depth/Surface Comparisons in Epileptic Subjects

Field potentials can be recorded from the human limbic system under the same task conditions that produce endogenous event-related potentials at the human scalp. In this chapter, recent findings are described that further support the local generation of the endogenous limbic potentials, the distributions of the limbic potentials are compared in auditory and visual tasks to evaluate the possibility of multiple endogenous components in the depth potentials, and clinical data are reviewed that bear on the issue of the limbic system as the neural source of the endogenous scalp potentials.

Phonological Processing and the Role of Strategy in Silent Reading: Behavioral and Electrophysiological Evidence

To examine the contribution of phonological processing in silent reading, 51 native English speakers made decisions about targets presented either in word pairs or in sentences. The target words were homophonically (plain-plane), orthographically (plane-place), or semantically (plane-jet) related. N200 was enhanced only to homophonic targets, suggesting the use of phonological information in silent reading. Memory load did not affect the N200 amplitude. N400 was enhanced to all semantically incongruent words and was larger in the word pair condition. Reaction times were influenced by both experimental condition and target relationships; homophonic stimuli elicited the fastest RTs in the word pair condition and the slowest RTs in the sentence condition, suggesting the use of different strategies. Thus, ERP components and behavioral responses registered different aspects of language processing.

The relation of P3b to prior events and future behavior

A prediction paradigm was used to explore the relationship of the amplitude of the scalp-recorded event-related potential to the sequence of preceding signals and to preceding and subsequent behavior. P3b was found to be the only component which related systematically to prior sequence of signals. The CNV, P300E and Slow Wave were not affected by signal sequence. The P3b findings were the same for the emitted and evoked P3b, thus ruling out a sensory interpretation of the effect of signal sequence on P3b amplitude. Furthermore, it was found that signal sequence interacts with the subjects predictions in determining P3b amplitude. For signal discontinuations, P3b was large in amplitude regardless of what had been predicted. However, for signal continuations, P3b was small when continuations had been predicted, but large when discontinuations had been predicted. Finally, we found that for both correctly and incorrectly predicted signal continuations, larger P3bs were more likely than smaller P3bs to be followed by a prediction that the signal for the next trial would be different.

Auditory event-related potentials during stage 2 NREM sleep in humans

SUMMARY  Event‐related potential (ERP) recordings were used to investigate the nature of auditory stimulus evaluation during stage 2 sleep. Frequent and rare stimuli, differing in intensity and frequency, were presented to six adult subjects while awake and asleep. The latency and voltage distribution of one of the long‐latency components evoked during sleep resembled the P3 component evoked while awake. However, it was attenuated in voltage and superimposed on N3, a large late negative component, most probably the slow potential of the K complex. The identification of a P3‐like potential during sleep suggests that the P3 potential is not solely a marker of active cognitive processes, but contains a small component which reflects automatic, pre‐attentive evaluation of deviant stimuli.

Sensitivity to monetary reward is most severely compromised in recently abstaining cocaine addicted individuals: A cross-sectional ERP study

Recent studies suggest that drug-addicted individuals have a dampened cortical response to non-drug rewards. However, it remains unclear whether recency of drug use impacts this impairment. Therefore, in this event-related potential study, recency of cocaine use was objectively determined by measuring cocaine in urine on study day. Thirty-five individuals with current cocaine use disorder [CUD: 21 testing positive (CUD+) and 14 testing negative (CUD-) for cocaine in urine] and 23 healthy controls completed a sustained attention task with graded monetary incentives (0¢, 1¢ and 45¢). Unlike in controls, in both CUD subgroups P300 amplitude was not modulated by the varying amounts of money and the CUD- showed the most severe impairment as documented by the lowest P300 amplitudes and task accuracy. Moreover, while recency of drug use was associated with better accuracy and higher P300 amplitudes, chronic drug use was associated with lower sensitivity to money. These results extend our previous findings of decreased sustained sensitivity to monetary reward in CUD+ to recently abstaining individuals, where level of impairment was most severe. Taken together, these results support the self-medication hypothesis, where CUD may be self-administering cocaine to avoid or compensate for underlying cognitive and emotional difficulties albeit with a long-term detrimental effect on sensitivity to non-drug reward.

Psychophysical measures of central auditory dysfunction in multiple sclerosis : neurophysiological and neuroanatomical correlates

Central auditory function was assessed in 15 patients with multiple sclerosis (MS) to determine whether the demyelinating lesions resulted in disruption of temporal processing. Auditory evoked potential (AEP) recordings included all three latency regions: Auditory brain stem responses (ABRs), midlatency responses (MLRs), and long-latency responses (LLRs). Two psychophysical tasks thought to involve temporal processing were used: a monaural-processing task (gap-detection) and a binaural-processing task (masking level difference; MLD). Further, AEP abnormalities and psychophysical performance deficits were related to lesion location, based on magnetic resonance imaging (MRI) scans. Reduced MLDs were seen in six MS subjects. Abnormal MLDs were always accompanied by abnormal ABRs and MLRs, and compared to subjects with normal MLDs, the subjects with abnormal MLDs were more likely to have bilateral abnormalities in the AEPs. Further, MLR indices of abnormal binaural interaction appeared to be specifically related to the psychophysical measure of binaural processing. The MRI data of these patients indicated widespread involvement of the auditory pathway. MS subjects with abnormal MRI signals restricted to levels caudal to the lateral lemniscus did not have abnormal MLDs. Gap-detection thresholds were more resistant to the effects of the demyelinating lesions; only two subjects had abnormal gap-detection thresholds. These subjects had extensive AEP abnormalities (bilaterally, in all three latency regions). The gap-detection thresholds were most specifically related to abnormalities of the LLRs. In addition, the subjects with elevated gap-detection thresholds were the only ones with a prolonged interval between the ABRs and MLRs. Thus, efficient neural conduction between the upper brain stem and auditory cortex appears to be crucial for normal monaural temporal processing. The results indicate that demyelinating lesions can cause deficits in temporal processing in the central auditory pathway. However, auditory temporal processing is not a unitary phenomenon since abnormalities at different levels of the auditory system disrupt different types of temporal processing. Finally, abnormal psychophysical performance was not seen in all subjects with AEP and MRI evidence of involvement of the auditory pathway; rather, these psychophysical measures appeared to be sensitive to disruption only in specific portions of the auditory system.

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

SUMMARY  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.

School and Neuropsychological Performance of Evacuated Children in Kyiv 11 Years after the Chornobyl Disaster

This paper examines the cognitive and neuropsychological functioning of children who were in utero to age 15 months at the time of the Chornobyl disaster and were evacuated to Kyiv from the 30-kilometer zone surrounding the plant. Specifically, we compared 300 evacuee children at ages 10-12 with 300 non-evacuee Kyiv classmates on objective and subjective measures of attention, memory, and school performance. The evacuee children were not significantly different from their classmates on the objective measures (grades; Symbolic Relations subtest of the Detroit Test; forms 1 and 2 of the Visual Search and Attention Test; Benton Form A; Trails A; Underline the Words Test) or on most of the subjective measures (the attention subscale of the Child Behavior Checklist completed by mothers; the attention items of the Iowa Conners Teachers Rating Scale; mother and child perceptions of school performance). The one exception was that 31.3% of evacuee mothers compared to 7.4% of classmate mothers indicated that their child had a memory problem. However, this subjective measure of memory problems was not significantly related to neuropsychological or school performance. No significant differences were found in comparisons of evacuees and classmates who were in utero at the time of the explosion, children from Pripyat vs. other villages in the 30-kilometer zone, and children manifesting greater generalized anxiety. For both groups, children with greater Chornobyl-focused anxiety performed significantly worse than children with less Chornobyl-focused anxiety on measures of attention. The results thus fail to confirm two previous reports that relatively more children from areas contaminated by radiation had cognitive deficits compared to controls. Possible reasons for the differences in findings among the studies are discussed.