Average Evoked Response Research Articles

Transcallosally evoked responses in the visual cortex of normal and monocularly enucleated rabbits.

In visual cortex of normal adult rabbits, callosal projections are restricted to a 2 mm wide band at the area 17/18 border. In adult rabbits which are monocularly enucleated (ME) on the day of birth, the callosal zone extends 4 mm into the medial region of area 17 in the cortex ipsilateral to the remaining eye. In this study, the function of these anomalous callosal projections in ME rabbits was investigated using electrophysiological techniques. A microelectrode was placed in the visual cortex ipsilateral to the enucleated eye at the 17/18 border, bipolar stimulating electrodes were placed in a homotopic location in the contralateral cortex, and averaged evoked responses (AERs) to stimulation were recorded. The stimulating electrodes were then moved mediolaterally in 1 mm steps, and the AERs were recorded for each location of the stimulating electrodes. In the normal rabbit, a maximal short latency evoked response was recorded when the stimulating electrodes were at a location homotopic to the recording electrode. When the stimulating electrodes were moved a distance of 1 mm or more from this optimal position, this short latency response was either absent or dramatically decreased in amplitude, reflecting the precise topographic pattern of the normal callosal projection. In contrast, in ME rabbits, a consistent response was evoked at the 17/18 border when the stimulating electrodes were moved as much as 3 mm medial to the homotopic position. Since antidromically activated responses and both pre- and postsynaptic orthodromically activated responses contribute to the AER, recordings were also made from single cells in some animals.(ABSTRACT TRUNCATED AT 250 WORDS)

An AER study of stop-consonant discrimination.

The purpose of this study was to explore hemispheric involvement in stop-consonant discrimination. Two experimental designs were used. In the first design, averaged evoked responses (AERs) to stop-consonant-vowel (CV) syllables were combined with AERs to nonspeech stimuli, in a paradigm similar to earlier studies, and were submitted to a principal components analysis and analyses of variance. In the second design, only the CV-syllable AERs were analyzed, in the same manner. When the responses to both CV and nonspeech stimuli were included in the analysis, the results were in agreement with those of earlier studies. However, when the nonspeech-stimuli AERs were removed from the analysis, the unilateral effects observed in prior studies were not replicated. The results of this research indicate the importance of considering experimental design and task variables before generalizing AER results to speech perception.

Cortical potentials evoked by innocuous tactile and noxious thermal stimulation in the rat: differences in localization and latency

Thermal stimulation of the rat hindleg at noxious intensities produced by laser-emitted radiant heat yielded replicable average evoked responses (AERs) in contralateral primary somatosensory cortex. In monopolar recordings, responses of opposite polarity were observed at the same depth at sites surrounding the point yielding maximum amplitude responses; potentials recorded at both central and surround sites reversed polarity in depth recordings. Compared to responses evoked by innocuous tactile stimulation, AERs to noxious thermal stimuli exhibited longer peak latencies, a more posterior localization, and a relatively higher amplitude negative component; all of these differences were statistically significant. These findings may reflect differences in central sensory mechanisms mediating the two types of stimuli and indicate the utility of the present technique for studying central mechanisms of pain perception.

AERs and detection in tasks yielding U-shaped backward masking functions.

ABSTRACTIn backward masking, psychophysical performance varies as a function of the interval between target and mask (stimulus onset asynchrony—SOA). Early studies of averaged evoked responses (AERs) and backward masking suggested a close, monotonic relationship, i.e., increasing psychophysical performance accompanied by increasingly larger AERs as a function of SOA. We asked what would happen to AERs if the perceptual task were designed to produce a U‐shaped performance function, i.e., one in which performance initially decreased and then increased as a function of SOA? In two experiments U‐shaped psychophysical performance was accompanied by monotonic AER functions. In a third experiment, comparing backward and forward masking at comparable SOAs, disparate psychophysical performances were obtained from the same subjects accompanied by similar AERs. Target AERs do not necessarily correlate with a subject's behavioral performance.

Platelet Mao Activity and Evoked Potentials in the Identification of Subjects Biologically at Risk for Psychiatric Disorders

Individuals potentially at risk for psychiatric disorders were identified by screening 375 college student volunteers for low platelet monoamine oxidase (MAO) activity levels. The lower and upper 10% in MAO activity were administered a personal and family history interview, psychological tests and average evoked response (AER) electroencephalographic procedures. Results indicated that low MAO males and females were socially more active, had more psychiatric contact, and had relatives who were psychiatrically more disturbed than high MAO subjects. Low MAO males had more convictions, experimented more with illegal drugs and had elevated scores on the MMPI. AER criteria further defined a high risk group of low MAO-AER augmenters which had more suicides among their relatives and higher scores on the schizophrenia scale of the MMPI.

Selective attention, channel capacity, and the Average Evoked Response in human subjects

Traditional studies of selective attention and the Average Evoked Response (AER) have employed naive subjects who performed non-verbal tasks designed to capture attention. The performance of highly trained subjects on a shadowing task, which is verbal in nature, reveals striking effects on the auditory AER which differ from those findings obtained with naive subjects. AER attenuation was found to be related to the level of the subject's sophistication in the performance of the task. Channel capacity is viewed as dynamic rather than fixed. Theoretical implications are discussed.

Influence of thalamic cooling on sensory responses in association cortex

O'BRIEN, J. H. AND S. M. ROSENBLUM. Influence of thalamic cooling on sensory responses in association cortex. BRAIN RES. BULL. 4(1) 91–98, 1979.—Evoked responses to light flash, click, and paw stimuli were recorded in the four cortical association areas in the acutely prepared cat. Average evoked responses (AEP) for 100 trials were formed before, during, and after localized cooling in the midline thalamus. Cooling of the midline thalamus reduced the magnitude of responses to click and paw stimuli, and increased or did not change the responses to light flash. There was very little similarity in trial-to-trial fluctuations of EP magnitude across cortical areas, and cooling did not reduce the similarity that existed. Waveform similarity was reduced by cooling for responses across the cortex to a single stimulus modality, whereas similarity of responses in a single cortical area to all three stimuli was not changed. The temporal components of the AEP influenced by thalamic cooling were different for different stimuli and cortical locations. It was concluded that the midline thalamo-cortical projection through the centromedian area to association cortices is particularly well-differentiated for multisensory responses in a single cortical region, and that the system should not be thought of as nonspecific but as convergent or multisensory.

Cognitive and evoked response measures of information processing in schizophrenics with and without a family history of schizophrenia.

Twenty-four male schizophrenics, 12 (SFH) with schizophrenia in the immediate family and 12 (SNFH) with no evidence of schizophrenia in the family background, and 24 male control subjects, 12 highly educated (HEC), and 12 minimally educated (MEC), were assessed for premorbid social adjustment and were administered the Digit Symbol Substitution Test, a size estimation task, and the EEG average evoked response (AER) at different levels of stimulus intensity. As predicted from the stimulus redundancy formulation, the SFH patients were poorer in premorbid adjustment, were less often paranoid, functioned at a lower level of cognitive efficiency (poor digit symbol and greater absolute error on size estimation), were more chronic, and, in some respects, had size estimation indices of minimal scanning. Contrary to prediction, the SFH group had the strongest and most sustained augmenting response on AER, while the SNFH group shifted from an augmenting to a reducing pattern of response. The relationship between an absence of AER reducing and the presence of cognitive impairment in the SFH group was a major focus of discussion.

Suicide attempts, platelet monoamine oxidase and the average evoked response

The relationship between suicides and suicide attempts and two biological measures, platelet monoamine oxidase levels (MAO) and average evoked response (AER) augmenting, was examined in 79 off-medication psychiatric patients and in 68 college student volunteers chosen from the upper and lower deciles of MAO activity levels. In the patient sample, male individuals with low MAO and AER augmenting, a pattern previously associated with bipolar affective disorders, showed a significantly increased incidence of suicide attempts in comparison with either non-augmenting low MAO or high MAO patients. Within the normal volunteer group, all male low MAO probands with a family history of suicide or suicide attempts were AER augmenters themselves. Four completed suicides were found among relatives of low MAO probands where as no high MAO proband had a relative who committed suicide. These findings suggest that the combination of low platelet MAO activity and AER augmenting may be associated with a possible genetic vulnerability to psychiatric disorders.

Auditory analgesia: somatosensory evoked response and subjective pain rating

Pain: June 1977 - Volume 3 - Issue 3 - p 287-288 doi: 10.1016/0304-3959(77)90024-0

Individual differences in average evoked responses to d- and l-amphetamine with and without lithium carbonate in depressed patients

Visual average evoked responses (AERs) to four intensities of light were studied in hospitalized depressed patients receiving placebo, d-amphetamine, l-amphetamine, lithium and d- and l-amphetamine combined with lithium. For the assessment of the subjective effects of the drugs, the patients completed a 34-item mood and behavior self-rating scale. AER responses to repeated doses of the amphetamines were consistent within the same individual but varied greatly between different individuals. For the patient group considered as a whole, only minor AER changes occurred in response to either d- or l-amphetamine; nonetheless, these minor changes were attenuated by lithium co-administration. There were indications, however, that AER baseline measures could be used as predictors of change in self-rating due to both d- and l-amphetamine, as patients who had larger AER amplitudes on baseline also tended to have larger increases in activation ratings and reductions in depression ratings. The amount of increase in AER amplitude or amplitude/intensity slope seen with amphetamine was also significantly correlated with the amount of increase in activation or euphoria ratings with amphetamine administration. These effects were most prominent in the same P100 component that we have previously found to differentiate bipolar and unipolar depressed patient groups.

Averaged evoked responses and the encoding of perception.

ABSTRACTThis paper reviews the hypothesis that averaged evoked response (AER) recordings encode the perception of stimulus content. AERs may be altered by changing subjects' expectancies, attention, affect, etc. AERs may also be altered by differences in the physical parameters of the eliciting stimuli. But if perception is viewed as the processing of the specific informational content of the stimuli, there is no convincing evidence that AERs encode perception. Thus, AKRs appear to be a summary of the activity of stimulus feature detectors and the results of decisions concerning the salience or importance of that information—AERs represent general operations not the specific content of the information being processed.

EVOKED RESPONSE AND KINESTHETIC MEASURES OF AUGMENTING/REDUCING IN SCHIZOPHRENICS

This study represents an attempt to replicate the central results of earlier work on stimulus intensity control. It uses a diverse sample of 40 hospitalized schizophrenic subjects, both chronic and acute. Two measures of stimulus intensity control were used: the Petrie kinesthetic figural aftereffects procedure (KFA), and the EEG method of average evoked response (AER). Finding the earlier results generally applicable, it presents a model of the function of stimulus intensity control in schizophrenia, which suggests that acute schizophrenics are particularly vulnerable to being inundated by stimuli, and therefore, that in order to protect themselves, they tend to reduce the perceived intensity of stimuli. Chronic schizophreniics have higher AER amplitudes and reduce less than acutes, suggesting that among chronics, the reducing mechanism either never was present or failed, whereas paranoid schizophrenics tend to be augmenters--a response style consistent with vigilant scanning.

Distinctive feature differences and the effect on the averaged evoked response

Subjects were habituated to a consonant-vowel-consonant (CVC) nonsense syllable, and were subsequently presented with a novel CVC. Response to the novel CVC was measured by averaged evoked response (AER). The novel stimuli were constructed by replacing the initial consonant with another consonant having 1, 2, or 3 distinctive feature differences. Differences in the AER were observed, dependent on the number of distinctive feature differences in the novel CVC. The discriminability of the minimally different CVC's will be discussed in light of the relationships between distinctive feature differences and the changes in the AER.

Average Evoked Response (AER) in the Electroencephalographic Diagnosis of the Normally Aging Brain: A Practical Application

Average Evoked Response (AER) in the Electroencephalographic Diagnosis of the Normally Aging Brain: A Practical Application

Auditory analgesia: somatosensory evoked response and subjective pain rating.

ABSTRACTSubjective rating responses and averaged evoked responses (AERs) to shock stimuli of varying intensity were recorded in 20 subjects to examine the possible analgesic effects of sound stimulation (music) and suggested analgesia. Subjects (10 men, 10 women, ages 19–31) were divided into two groups of 10, each receiving the sound‐suggestion condition and the no‐sound, no‐suggestion condition in different order. Sound and suggestion produced the following significant (p<.05) effects: 1) increased electrical stimulus levels required to elicit discomfort ratings; 2) decreased slope of somatosensory AER amplitudes plotted against stimulus intensity; and 3) decreased mean AER amplitudes. These AER effects were greatest in time bands centered on the P100 component. Prior exposure to the electrical stimuli also reduced AER slopes and mean amplitudes, but mostly in time bands centered on the P200 component.

Intravenous l-DOPA plus carbidopa in depressed patients: average evoked response, learning, and behavioral changes.

The peripheral decarboxylase inhibitor carbidopa (L-alphamethyl-dopa-hydrazine) allowed safe intravenous administration of L-DOPA in amounts sufficient to alter cortical average evoked response (AER) and learning function in 13 depressed patients. The apparently rapid conversion of L-DOPA to dopamine, as reported from studies in animals, is consistent with the 20-30 min onset of effects seen in our study. Unipolar and bipolar depressed patients responded differently to the alterations in brain biogenic amines and also to the nonspecific stress of the experiment. Intravenous L-DOPA given acutely had effects on the AER that were similar to those documented with oral dopa given chronically--an augmentation of amplitude--intensity slopes in unipolar patients and a relative reduction of slopes in bipolar patients. In contrast, intravenous L-DOPA did not enhance verbal learning as did chronic oral treatment, but rather was associated with reduced learning compared with placebo infusions. Different neurochemical changes following L-DOPA given in single intravenous doses may be responsible for the different learning and behavioral changes form those found previously with oral dopa administered chronically.

Évolution des réponses évoquées le long de la voie visuelle au cours du sommeil nocturne chez Papio papio

Averaged evoked responses (AER) to light flashes were recorded in baboons ( Papio papio) during wakefulness, slow-wave sleep and rapid eye movement (REM) periods, at the visual cortex, retrocalcarine sulcus, optic tract (OT), lateral geniculate (LG) and pulvinar. Waking AERs were composed: in the OT, of a negative, low amplitude wave at 13.3 msec (I), a high amplitude wave at 34.8 msec (II), a negative wave at 72 msec (III) and a late component at 151 msec; in the LG, a small positive wave (II) with a peak latency of 40 msec, a high amplitude negative wave (III) with a latency of 70 msec and a late component; in the pulvinar of two low amplitude short latency waves (I and II), respectively negative and positive at 25 msec and 40 msec, then a high amplitude negative wave (III) at 75 msec and a late component; in the retrocalcarine sulcus 3 positive waves (I, II and III) were recorded at 25, 45 and 100 msec and a late component; in the visual cortex, 3 low amplitude negative waves (II, III and IV) at 40, 50 and 54 msec, then a positive wave at 80 msec and some late components. In slow-wave sleep, AERs did not change in the OT, but in the LG and pulvinar, they showed an increase in the amplitude of wave II from stage 1 to stage 3. At the cortical level, early waves (II for the retrocalcarine sulcus, II and IV for the visual cortex) presented a marked increase in amplitude during stages 2 and 3, but only a slight increase for stage 1. Peak latency increase of each wave in cortical and subcortical AERs was seen during slow-wave sleep. REM AERs resembled, in amplitude and peak latency, those recorded in the LG and pulvinar during wakefulness; in the visual cortex and retrocalcarine sulcus, they were similar to those obtained during wakefulness and stage 1. In conclusion, a different evoked response was found between visual cortex and deep structures (except for the OT): firstly, during slow-wave sleep (the AERs showed a difference for stage 1 between the visual cortex or the retrocalcarine sulcus and the LG or the pulvinar), secondly, in REM (on the cortex, REM AERs looked like wakefulness and stage 1 responses); on the contrary, in the LG and pulvinar, REM AERs were similar only to those recorded during waking. Finally, it can be said that for Papio papio the differentiation and structural responses between the various stages of sleep (particularly light sleep and REM) were greater in the cortex than in the thalamic structures.

Effect of Sleep Stage and Stimulus Intensity on Auditory Average Evoked Responses

ABSTRACTAuditory average evoked responses (AERs) to clicks ranging from 50 to 80 dB were studied in 9 normal adults while awake and during sleep. AER amplitude tended to increase little from 50 to 80 dB in waking subjects but increased markedly in sleeping subjects during stages 3 and 4. Rapid eye movement (REM) and stage 1 sleep had small amplitude AER.S in comparison with other sleep stages, individuals who showed decreases in amplitude at high intensities while awake slept significantly longer during the experimental nights.

Schizophrenia and stimulus intensity control.

A group pf 19 acute, medication-free schizophrenic patients was studied, using average-evoked responses (AERs) to four intensities of light. Comparison with age- and sex-matched normal controls and patients with bipolar affective disorders showed that schizophrenics had smaller AER amplitudes and either no increase or an actual decrease in amplitude with increasing stimulus intensity. Normal subjects and schizophrenic patients were discriminated with 71% accuracy using AER variables; normals, patients with bipolar disorders, and schizophrenic patients with 64% accuracy. Patients who evidenced this AER "reducing" pattern to a noticeable extent early in hospitalization showed greater improvement and tended to have relatively good premorbid histories.