Cortical evoked responses to synonyms and antonyms

The brain’s processing of synonymity and antonymy was explored by examining the cortical evoked responses to correct judgments that a test word was a synonym or an antonym of a standard word presented 1 sec previously. Each of five subjects judged 256 pairs of words in each of two sessions. The evoked response to the second word was averaged separately for synonym and antonym pairs. Presentation of each test word as a synonym or an antonym, the order of presentation of each pair, and the side of the “synonym” response key were counter-balanced within subjects. The difference between the averaged response to antonym test words and that to synonym test words differed biphasically over the interval 250-650 msec after the stimulus. The demonstration of an evoked response difference between synonyms and antnyms extends the applicability of evoked potentials from attributes of individual word meaning to the semantic relationships between words.     

State-dependent variations in brainstem auditory evoked responses in human subjects

BAERs from 16 subjects during 3 sessions varied in the latency or amplitude of some components depending upon level of arousal as indicated by EEG patterns. There was a general tendency for activation to produce the fastest responses with the largest amplitudes and for drowsiness to produce the slowest responses with the smallest amplitudes. The latency of P2 was significantly prolonged during drowsiness, relative to those during relaxation or activation. For right-ear stimulation, P5 latency was longest during drowsiness, and shortest during activation while for left-ear stimulation the shortest latency occurred during relaxation. The amplitudes of Wave II and Wave VII were significantly smaller during drowsiness than during activation. Although the differences were below the level of clinical significance, the data indicate a modification in the characteristics of brainstem transmission as a function of concurrent activity in other brain areas.     

A technique for quantifying and analyzing evoked responses

Two computer programs are discussed. One is used in the analog-to-digital conversion of and averaging of the responses; the other employs fuil-wave rectification and numerical integration as a method of comparing waveforms.     

Attention and auditory evoked responses to low-detectability signals

Comparisons were made between cortical evoked responses obtained under two conditions: (1) while Ss were reading, and (2) while they were attempting to count auditory signals. The amplitudes of evoked responses to low-detectability auditory stimuli were found to be approximately doubled when the Ss were required to count the number of stimuli, as compared to amplitudes recorded when they were reading. The duration of the response was also markedly increased. These increases in response amplitude and duration are considerably greater than those observed in earlierexperiments, where high-levelsignalswere used. Inter-S variability of the waveform of the averageevoked response was observed to be much less when the Ss counted the stimuli. In another experiment the level of the auditory signalwas varied over a range of approximately +4 to -4 decibels relative to the listeners’ behavioral thresholds. The per cent of signalswhich they counted varied from near-zero to 100, over this range, and the evoked response concurrently showed a variation from “unmeasureable” to approximately 8 microvolts.     

Variation in cortical evoked responses as a function of performance criterion

Averaged evoked cortical responses (CER) from the scalp of human Ss were recorded within an experimental paradigm that permitted the performance criterion to be varied. The signals evoking the cortical responses were contingent upon S’s pressing a button to bisect a temporal interval within certain tolerance limits. Under passive conditions averaged response waveforms lacked a second, late component that became prominent under temporal bisection conditions. The late component P² - N² increased regularly in magnitude as the performance criterion was made more stringent. The effect of performance criterion on the earlier component, N¹ - P², was neither as large nor as systematic as that shown by P² - N².     

The effect of smoking on brainstem auditory evoked potentials in positive- and negative-symptom schizophrenia

Studying brainstem auditory evoked potentials (BAEPs) and comparing the specific waves in smokers vs nonsmokers in both positive- and negative-symptom schizophrenia may elucidate the role of smoking in information processing. BAEPs were recorded in 40 patients with schizophrenia; 20 had predominantly positive symptoms (10 smokers and 10 nonsmokers) and 20 had predominantly negative symptoms (10 smokers and 10 nonsmokers). The severity of positive and negative symptoms was assessed by scale of assessment of positive symptoms and scale of assessment of negative symptoms (SANS). The BAEP results were compared with 15 healthy control individuals matched with the patients by age, sex, and cultural background. The smokers with negative symptoms showed a significant increase in the alogia, summary, and composite scores of SANS as compared to the nonsmokers. Although, most of the BAEP abnormalities were among patients with positive symptoms. The effect of smoking on the BAEPs was only in patients with negative symptoms. We also studied the interaction between smoking factor (smokers vs nonsmokers) and group type (group with mostly positive symptoms vs group with mostly negative symptoms) on the BAEPs and found a significant difference only for the first-wave latency mainly on the right side (P=0.012). The absence of a significant effect of smoking on most of the parameters of the BAEPs on interaction with the group factor suggests that the effect of smoking on the BAEPs is more apparent when negative symptoms prevail. However, studies are warranted to substantiate this finding.     

Neonatal auditory evoked responses are related to perinatal maternal anxiety

Maternal stress and anxiety during pregnancy are related to negative developmental outcomes for offspring, both physiological and psychological, from the fetal period through early adolescence. This robust relationship is likely to be partly explained by alterations in fetal neurodevelopmental programming, calling for further examination of neurophysiologically-based cognitive markers that may be related to the altered structure–function relationships that contribute to these negative developmental outcomes. The current investigation examined the relationship between perinatal maternal anxiety and neonatal auditory evoked responses (AERs) to mother and stranger voices. Results indicated that neonates of low-anxiety mothers displayed more negative frontal slow wave amplitudes in response to their mother’s voice compared to a female stranger’s voice, while neonates of high-anxiety mothers showed the opposite pattern. These findings suggest that neonates of perinatally anxious mothers may demonstrate neurophysiologically-based differences in attentional allocation. This could represent one pathway to the negative psychological outcomes seen throughout development in offspring of anxious mothers.     

Human visual evoked responses are related to heart rate.

The purpose of the present experiment was to determine the relation between changes in heart rate and averaged evoked potentials. Sixteen male subjects with variable heart rates received 50 flashes of light during fast heart beats, 50 during slow heart beats, and 50 during midrange heart rate level. Evoked responses were recorded from the scalp overlying the right and left occipital lobes. Heart rate, respiration, eye movements, and cephalic blood flow were also recorded. The results indicated that spontaneous changes in heart rate are related to changes in visual evoked responses and that this relation differs for the two cerebral hemispheres. Furthermore, cephalic pulse amplitude was largest following slow heart beats and smallest following fast heart beats, which suggests that changes in heart rate are related to changes in cerebrovascular as well as electrocortical activity. The results are discussed in terms of formulations derived from behavioral studies regarding the relation between cardiovascular activity and attentional processes.     

Auditory evoked brain responses: Comparison of ON and OFF responses at long and short durations

Average evoked brain responses (EBRs) to three durations of one kilohertz pure-tone stimuli were computed from human scalp recordings. Stimuli of 25, 75, and 2,000 msec duration were each presented binaurally at each of eight equally spaced intensity levels, ranging from 58 to 86 dB SPL. EBRs computed immediately following presentation, and immediately following removal of the 2,000-msec-duration stimulus result in ON and OFF responses, respectively. EBRs computed immediately following presentation of the 25- and 75-msec-duration stimuli appear to be the result of the sum of separate responses to stimulus onset and offset. Computer-dissected ON and OFF EBRs to short-duration stimuli are very similar in waveform and amplitude to the responses evoked by the onset and offset, respectively, of the 2,000-msec duration stimulus. Dissected ON and OFF responses demonstrate linear amplitude-intensity functions in amplitude ranges similar to respective ON and OFF responses to 2,000-msec stimulation. The data suggest that ON and OFF responses are mediated by independent physiological mechanisms.     

Power functions of loudness magnitude estimations and auditory brainstem evoked responses

The correspondence between subjective and neural response to change in acoustic intensity was considered by deriving power functions from subjective loudness estimations and from the amplitude and latency of auditory brainstem evoked response components (BER). Thirty-six subjects provided loudness magnitude estimations of 2-sec trains of positive polarity click stimuli, 20/sec, at intensity levels ranging from 55 to 90 dB in 5-dB steps. The loudness power function yielded an exponent of .48. With longer trains of the same click stimuli, the exponents of BER latency measures ranged from -.14 for wave I to -.03 for later waves. The exponents of BER amplitude-intensity functions ranged from .40 to .19. Although these exponents tended to be larger than exponents previously reported, they were all lower than the exponent derived from the subjective loudness estimates, and a clear correspondence between the exponents of the loudness and BER component intensity functions was not found.     

Eye movements,evoked responses and visual perception: Some speculations

In a number of studies dealing with the activity of the visual system it has been found that the duration of 250–300 msec appears to be critical in some manner. It is suggested that these findings (from studies dealing with fixation durations during visual search, evoked cortical potential patterns, and the temporal limitations in the visual perception of sequential events) may be related to certain aspects of the processing and assimilation of visual information.     

Auditory evoked brain responses: Intensity functions from bipolar human scalp recordings

Average evoked brain responses were computed from four simultaneous recordings during binaural tone stimulation at 10 intensity levels. Amplitudes and latencies were measured for the prominent components, and linear regression coefficients were computed. The results indicate that the sensitivity of the evoked response to stimulus intensity is dependent upon the selection of the appropriate measure. Linear amplitude functions were demonstrated. Additional research relating these responses to psychophysical measures is suggested.     

Controlled information processing resources and the development of automatic detection responses in schizophrenia

The relation between resource limitations and the type of processing (automatic vs. controlled) on a multiple-frame search task (MFST) was examined in 15 schizophrenic and 15 normal control subjects. After 320 trials of consistently mapped practice, the patients' detection accuracy was normalized, and the effect of processing load (letter array size) on their detection accuracy was eliminated, which suggests automatization. Changes in load effects with practice could not be used as an index of automatization in control subjects, because of their unexpected lack of load effects at the beginning of practice. In a dual-task (MFST during auditory shadowing) condition after MFST practice, patients' MFST accuracy deteriorated nonsignificantly, and patients' shadowing declined significantly. The findings suggest schizophrenics have reduced available processing resources, but research is needed to determine whether this is due to abnormal automatization.     

Antipsychotic dose modulates behavioral and neural responses to feedback during reinforcement learning in schizophrenia

Schizophrenia is characterized by an abnormal dopamine system, and dopamine blockade is the primary mechanism of antipsychotic treatment. Consistent with the known role of dopamine in reward processing, prior research has demonstrated that patients with schizophrenia exhibit impairments in reward-based learning. However, it remains unknown how treatment with antipsychotic medication impacts the behavioral and neural signatures of reinforcement learning in schizophrenia. The goal of this study was to examine whether antipsychotic medication modulates behavioral and neural responses to prediction error coding during reinforcement learning. Patients with schizophrenia completed a reinforcement learning task while undergoing functional magnetic resonance imaging. The task consisted of two separate conditions in which participants accumulated monetary gain or avoided monetary loss. Behavioral results indicated that antipsychotic medication dose was associated with altered behavioral approaches to learning, such that patients taking higher doses of medication showed increased sensitivity to negative reinforcement. Higher doses of antipsychotic medication were also associated with higher learning rates (LRs), suggesting that medication enhanced sensitivity to trial-by-trial feedback. Neuroimaging data demonstrated that antipsychotic dose was related to differences in neural signatures of feedback prediction error during the loss condition. Specifically, patients taking higher doses of medication showed attenuated prediction error responses in the striatum and the medial prefrontal cortex. These findings indicate that antipsychotic medication treatment may influence motivational processes in patients with schizophrenia.