Event-related potential correlates of proactive interference in schizophrenic patients and controls

Performance and event-related potentials (ERPs) were examined in a proactive interference (PI) task with 15 male schizophrenic patients and 15 matched healthy controls. Within a paired-associate task, 30 pairs of semantically unrelated words (A-B) were presented twice, followed by cued recall, in which the paired-associate B had to be named upon cue A. Subsequently, 50% of the A-words were paired with new words (A-C) and presented in random order together with 15 novel pairings (D-E). Slower responses and poorer recall of C- than of E-words in the final recall indicated PI in both groups. During acquisition, the paired-associates (C/E) evoked larger P3 and positive slow wave in controls than in patients. During recall, cues (A/D) evoked a slow wave with predominating anterior negativity in controls and posterior positivity in patients. The group-specific ERP pattern suggests deviant encoding and retrieval processes in schizophrenic individuals.

Failure of dominant left-hemispheric activation to right-ear stimulation in schizophrenia

Schizophrenia is associated with an absence of the lateralizations that typify the human brain. Previous evidence emphasized structural changes, particularly reduced asymmetry in extension and surface of the planum temporale, although gross structural deviations occur only in a minority of patients. The present study describes an absence of lateralization on a robust functional measure that characterized schizophrenia patients: healthy subjects but not schizophrenics displayed a contralateral left-hemispheric dominance of the auditory evoked magnetic field to right-ear auditory stimulation. Absence of contralateral dominance in response to auditory stimuli among schizophrenia patients may indicate a failure to establish unequivocal left-hemispheric dominance of the phonological loop as hypothesized by Crow.

Alteration of digital representations in somatosensory cortex in focal hand dystonia

Focal hand dystonia involves a loss of motor control of one or more digits; it is associated with the repetitive, synchronous movements of the digits made by musicians over periods of many years. Magnetic source imaging revealed that there is a smaller distance (fusion) between the representations of the digits in somatosensory cortex for the affected hand of dystonic musicians than for the hands of non-musician control subjects. The data suggest that use-dependent susceptibility to digital representation fusion in cortex may be involved in the etiology of focal dystonia. A successful therapy for the condition has been developed based on this consideration.

Dynamical aspects of motor and perceptual processes in schizophrenic patients and healthy controls

The present study examined the temporal stationarity of the performance of 16 schizophrenic patients and 16 controls matched for age and sex in a bimanual coordination task and a perceptual task. In the motor task, rhythmic finger oscillations (alternating activity of homologue muscle groups) at increasing speed levels resulted in two measures, the preferred oscillation frequency and the critical frequency at which phase transitions (change towards simultaneous activity of homologue muscle groups) occurred. A measure of local dimensional complexity (pointwise D2 or PD2), which is a measure of non-linear dynamics, was determined for the acceleration profiles of the subjects' movements. Schizophrenics exhibited less stable movement dynamics than controls in horizontal finger cycling, indicated by a lower ratio critical/preferred frequency (critical ratio) and by higher means and standard deviations of the pointwise D2. In vertical cycling, the critical ratio did not differentiate between groups, while PD2 means and standard deviations did. Groups also differed specifically in perception of two ambiguous figures (Schroeder stairs and Rubin vase). Schizophrenics showed significantly higher reversal rates for the Rubin vase and a differential perceptive in comparison to controls in the perception of the Schroeder stairs. Measures of perceptual and motor stability were unrelated, which suggests that perceptual and motor processes are not influenced by a common underlying mechanism.

Monitoring brain activity of human subjects during delayed matching to sample tasks comparing verbal and pictorial stimuli with modal and cross-modal presentation: an event related potential study employing a source reconstruction method

The time course of the event related potentials evoked within a delayed matching to sample task employing verbal and pictorial stimuli was analyzed with a source reconstruction method (minimum norm method). During signal stimulus presentation pictorial stimuli evoked more activity than verbal stimuli. Activity was particularly prominent in left frontal areas for the match of verbal-verbal stimulus pairs and over right posterior regions for the match of verbal-pictorial stimuli. Anticipation of the to-be-matched stimulus produced more pronounced activity for pictorial stimuli and generally stronger left and frontal activity. Results are discussed referring to a biological model of language processing.

Perceptual correlates of changes in cortical representation of fingers in blind multifinger Braille readers

The mature mammalian nervous system alters its functional organization in a use-dependent manner. Enhanced stimulation of a body part enlarges its cortical representational zones and may change its topographic order. Little is known about the perceptual and behavioral relevance of these plastic alterations in cortical organization. We used blind Braille readers who use several fingers on each hand and who do so for many hours each day as a model to investigate this issue. Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in these subjects; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus. In contrast, neither the disordered representation nor mislocalizations were observed in sighted controls. Blind non-teacher Braille readers who used only one finger for reading were not significantly different from the sighted controls. Thus, use-dependent cortical reorganization can be associated with functionally relevant changes in the perceptual and behavioral capacities of the individual.

Topography of CNV and PINV in schizotypal personality

The topography of the postimperative negative variation (PINV) was analyzed in participants with high and low scores on the German version of the Schizotypal Personality Questionnaire. Scalp amplitude and Laplacian maps of the terminal contingent negative variation (tCNV) and PINV and the time course of the PINV were compared between the two groups. CNV and PINV were induced with a delayed matching-to-sample task, in which the pattern of the imperative stimulus was either clearly or ambiguous matched to one of the two diamonds simultaneously presented as a warning stimulus 4.0 s earlier. Electroencephalograms were recorded with a DC amplifier (32 channels). Negativity increased from tCNV to PINV, especially at frontal sites, and the PINV was larger under ambiguous than under clear matching conditions. Low-scoring participants showed a right-sided predominance of the PINV, which was absent in high-scoring participants. These results resemble differences in the topography of the PINV between healthy control participants and those with schizophrenia under identical experimental conditions and suggest functional differences between tCNV and PINV.

Study of the human auditory cortices using a whole-head magnetometer: left vs. right hemisphere and ipsilateral vs. contralateral stimulation

Structural and functional asymmetries of the temporal lobe affect language development and may also play a role in a variety of disorders, ranging from specific language impairment to schizophrenia. Whole-head neuromagnetometers allow the noninvasive measurement of functional asymmetries since activity from both hemispheres is recorded simultaneously. In the present study, the location of the auditory cortices and their responsiveness to pure tones was compared between hemispheres in healthy human subjects. Data suggest a greater contralateral than ipsilateral activation. In line with previous findings, sources of responses for the right hemisphere seem to be more anterior than for the left one.

Dynamical aspects of the EEG in different psychopathological states in an interview situation: a pilot study

Dynamical brain states can be characterized by non-linear measures of EEG. The present study shows that critical transitions, i.e., abrupt changes from one dynamic pattern of neural mass activity to another one, may be detected by abrupt variations in local chaoticity. Using an ambulatory device, EEG was recorded from 10 patients with a schizophrenic and two patients with an affective disorder during a series of 25-min interviews. Dynamical aspects, in particular, phase transitions in the EEG-dynamics of the EEG were characterized by means of a measure that continuously estimates the chaoticity of the EEG signal and is thus related to its predictability. Results indicate simpler dynamics of the EEG time series in paranoid-hallucinatory patients, while at the same time these patients tended to exhibit more abrupt transitions/unit of time between different dynamical EEG states. Such sudden phase transitions in brain activity were significantly enhanced prior to expressions of thought disorders that were detected by the interviewer and an observer in the conversation, compared with time periods during the interview without such symptoms.

Input-increase and input-decrease types of cortical reorganization after upper extremity amputation in humans

A plastic remodeling of regions in somatosensory cortex has previously been observed to occur in separate experimental paradigms in response to loss of somatosensory input and to increase in input. In this study, both types of cortical reorganization have been observed to occur concurrently in the same adult human nervous system as a result of a single intervention. Following upper extremity amputation, magnetic source imaging revealed that tactile stimulation of the lip evoked responses not only in the area of the somatosensory cortex corresponding to the face, but also within the cortical region that would normally correspond to the now absent hand. This "invasion" of the cortical amputation zone was accompanied by a significant increase in the size of the representation of the digits of the intact hand, presumably as a result of an increased importance of sensory stimulation consequent to increased dependence on that hand imposed by the loss of the contralateral extremity.

Mapping EEG-potentials on the surface of the brain: a strategy for uncovering cortical sources

This paper describes a uniform method for calculating the interpolation of scalp EEG potential distribution, the current source density (CSD), the cortical potential distribution (cortical mapping) and the CSD of the cortical potential distribution. It will be shown that interpolation and deblurring methods such as CSD or cortical mapping are not independent of the inverse problem in potential theory. Not only the resolution but also the accuracy of these techniques, especially those of deblurring, depend greatly on the spatial sampling rate (i.e., the number of electrodes). Using examples from simulated and real (64 channels) data it can be shown that the application of more than 100 EEG channels is not only favourable but necessary to guarantee a reasonable accuracy in the calculations of CSD or cortical mapping. Likewise, it can be shown that using more than 250 electrodes does not improve the resolution.

The postimperative negative variation following ambiguous matching of auditory stimuli

Previous studies using the delayed-matching-to-sample paradigm with visual stimuli reliably induced a postimperative negative variation (PINV) in both schizophrenic patients and healthy controls. The PINV was found to be: (a) larger in schizophrenic patients than controls; (b) larger under conditions of ambiguous as compared to clear matching conditions; and (c) larger over right-hemispheric, fronto-temporal regions in controls, while a less asymmetrical distribution with a tendency for left-frontal predominance occurred in schizophrenic patients. The present study examined to what extent the development and scalp distribution of the PINV were modality-specific by applying the delayed-matching-to-sample design using auditory stimuli. Furthermore, the neurophysiological state during anticipatory negativity (CNV) and PINV was examined by presenting acoustic probe stimuli (one per trial on 50% of the trials) during baseline, CNV or PINV interval. Event-related slow and probe-evoked potentials were recorded in 13 patients with a chronic schizophrenic disorder (DSM-III-R) and 13 healthy control Ss from 15 electrode sites including midline and two sagittal rows over each hemisphere. Comparable group differences and effects of ambiguity on PINV amplitudes were found for both modalities, visual and auditory. The auditory stimuli produced a fronto-central distribution of the PINV in both groups. The probe-evoked vertexpotential was smaller in patients compared to controls, but exhibited comparable modulation with the largest amplitude during the CNV in both groups. Results suggest modality-non-specific cognitive determinants of the PINV. However, stimulus modality did affect the scalp distribution of the PINV. Probe-evoked responses point to different functional meaning of negativities prior to (CNV) and following (PINV) task-relevant stimuli.

[Visually-induced gamma band responses in human EEG- expression of cortical stimulus representation?]

The features of a visual stimulus are processed in different regions of the visual cortex with no direct axonal connections. Therefore, neurons in the distributed processing areas must be connected in some way to form the physiological substrate of the percept. On the basis of theoretical considerations and animal experiments, it has been proposed that synchronization of neuronal oscillatory firing patterns in the gamma band range (above 30 Hz) might be essential in linking the anatomically distant cell assemblies that represent the various features of the stimulus. The present work reports on three experiments in which the functional relevance of induced gamma band responses were investigated in the human EEG. Using an identical stimulation design, as used in animal studies, it was demonstrated that human induced gamma band responses resembled those reported from intracortical recordings from animals. It was further shown that alpha and gamma band activities differed in temporal characteristics as well as in topographical features, indicating the representation of different cortical functional states. In accordance with previous animal and human experimental findings, a complex moving stimulus was related to a suppression of induced gamma band activity as opposed to a standing complex stimulus.

Visually induced gamma-band responses in human electroencephalographic activity--a link to animal studies

Visual presentation of an object produces firing patterns in cell assemblies representing the features of the object. Based on theoretical considerations and animal experiments, it has been suggested that the binding of neuronal representations of the various features is achieved through synchronization of the oscillatory firing patterns. The present study demonstrates that stimulus-induced gamma-band responses can be recorded non-invasively from human subjects attending to a single moving bar. This finding indicates the synchronization of oscillatory activity in a large group of cortical neurons. Gamma-band responses were not as apparent in the presence of two independently moving stimuli, suggesting that the neuronal activity patterns of different objects are not synchronized. These results open a new paradigm for investigating the mechanisms of feature binding and association building in relation to subjective perception.

Cortical sources of human short-latency somatosensory evoked fields to median and ulnar nerve stimuli

;;;;;õry evoked magnetic fields were measured with a 122-channel whole-scalp neuromagnetometer from seven healthy adults. Electric stimuli, with an intensity above the motor threshold, were delivered once every 0.5 s alternately to the median and ulnar nerves at the wrist; both wrists were stimulated successively within one session. In most subjects, two distinct neural sources were identified at the contralateral primary somatosensory cortex SI for both stimuli. The first source (M20) peaked at 21-22 ms and indicated activation of area 3b in the contralateral SI hand region. The same source peaked with opposite current direction at 32 ms. The second source (M40) was slightly medial to M20 and exhibited two peaks with the same current direction, first at 25 ms and most prominently at 42 ms. M20 was on average 7 mm more lateral along the central sulcus for median than ulnar nerve stimuli, in agreement with the somatotopic organization of the SI cortex; similar organization for M40 was less clear. These results suggest that M20 and M40 to upper limb stimulation represent activation of distinct neuronal populations in hand SI cortex, presumably in area 3b.

Contingent negative variation (CNV) and determinants of the post-imperative negative variation (PINV) in schizophrenic patients and healthy controls

A slowly rising cortical potential shift with negative polarity following the imperative stimulus of a forewarned reaction time task, the 'post-imperative negative variation' (PINV), is regularly observed in schizophrenic patients but not in controls. The topography of the PINV suggests that it may originate in frontal cortical regions. We used a task designed to test two putative prefrontal cortical functions: working memory and processing of ambiguity. Nineteen patients with a chronic schizophrenic disorder and 19 control subjects matched for age, sex, and education participated in two experimental sessions. The EEG was recorded from frontal, central, temporal, and parietal leads over both hemispheres using a DC amplifier. PINV amplitudes were generally larger in patients than in controls. If the result of comparing physical features of the two successively presented stimuli (warning and imperative stimulus) was ambiguous rather than clear, an augmentation of the PINV amplitudes was seen in both groups. If this comparison required high rather than low involvement of working memory functions, PINV amplitudes were augmented in schizophrenic patients only. Scalp distribution of the PINV indicated a left-hemisphere fronto-central PINV maximum in patients, and a right-hemisphere predominance in controls, which was larger following ambiguous stimulus comparisons. These results suggest that ambiguity during the comparison of physical features of successively presented stimuli may be a general factor of the PINV in schizophrenic patients and healthy controls. Augmented involvement of working memory functions, presumably subserved by the prefrontal cortex, specifically affected the fronto-centrally predominant PINV in schizophrenic patients. This result is compatible with the hypothesis of prefrontal cortical dysfunctions in schizophrenia.

Effects of voluntary movements on early auditory brain responses

It has not been clear whether or not early information processing in the human auditory cortex is altered by voluntary movements. We report a movement-related, complex event-related potential consisting of relatively long-lasting amplitude and phase perturbations induced in an ongoing auditory steady-state response (SSR) by brief self-paced finger movements. Our results suggest that processing in the auditory cortex during the first 50-100 ms after stimulus delivery is affected before, during, and after voluntary movements, beginning with a 1- to 2-ms delay in the SSR wave form starting 1-2 s before the movement.

The impact of performance uncertainty on the postimperative negative variation

In a delayed matching-to-sample task, the impact of clear or ambiguous go versus clear no-go signals on the post-imperative negative variation (PINV) was examined in 11 patients with a chronic schizophrenic disorder (DSM-III-R) and in a control group of 13 healthy subjects matched to the patient sample by age, sex, and education. Size and spatial position of a visual S2 had to be matched to one of two visual patterns in the S1 presented 4 s earlier. In 96 trials, the S2 was identical in size with one of the two patterns of S1 (clear matching). These trials varied pseudorandomly, with 60 trials in which the S2 was of intermediate size. On a randomly interspersed additional 48 trials, an S2 differing in color and shape signaled no-go. The electroencephalogram was recorded from Fz, Cz, Pz, F3, F4, C3, C4, P3, and P4. Although groups did not differ in contingent negative variation amplitude, the PINV was generally more pronounced in patients than in controls. In both groups, ambiguity of the to-be-matched S2 produced larger PINV amplitudes; the no-go signal elicited only a small PINV. Differential effects of ambiguity and no-go on PINV amplitude and its scalp distribution suggest that "performance" and "action" uncertainty contribute to PINV generation and that thresholds for both effects are reduced in schizophrenics.

Modulation of auditory responses during oddball tasks

The modulation of auditory input processing in relation to slow event-related potentials was examined in two studies. A steady-state response (SSR) was evoked by a stimulus train delivered at 40 Hz. Slow potentials were elicited by an oddball task implemented as changes in the pitch of single stimuli within this 40-Hz train. In study 1, subjects responded to rare targets by means of a button press. In study 2, subjects responded to targets by means of a motor response in one session and by silent counting in another session. In both studies, the oddball task elicited a P300 to targets. SSR amplitude was reduced 100 ms following each stimulus, while a second amplitude reduction around 350-400 ms was discovered following targets, in particular, following a button press. Parallel to SSR amplitude reductions, the latencies between stimulus and subsequent SSR peak were reduced. Results indicate that processing of oddball stimuli and motor responding alters 'automatic' auditory processing at the level of the primary auditory cortex; the second SSR amplitude reduction which develops in parallel to P300 might support the hypothesis that slow positive potentials indicate widespread (disfacilitation) inhibition of cortical neural excitability.

Increased cortical representation of the fingers of the left hand in string players

Magnetic source imaging revealed that the cortical representation of the digits of the left hand of string players was larger than that in controls. The effect was smallest for the left thumb, and no such differences were observed for the representations of the right hand digits. The amount of cortical reorganization in the representation of the fingering digits was correlated with the age at which the person had begun to play. These results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.

Event-related and motor responses to probes in a forewarned reaction time task in schizophrenic patients

Surface-negative brain potentials indicate increased excitability of the underlying cortical neural networks. Consequently, deviant patterns of event-related potentials in schizophrenic patients reveal an atypical regulation of cortical excitability. Twelve patients with a chronic schizophrenic disorder and 12 matched control subjects were investigated using a probe paradigm: A contingent negative variation (CNV) was evoked in a forewarned reaction time paradigm. Clicks were presented before, during and after elicitation of the CNV. Click-evoked responses allow one to 'probe' the current brain state, particularly neuronal excitability, which is also reflected by the slow potentials. During the measurements, subjects pressed one button in response to the offset of the visual warning stimulus and a different button in response to the acoustic probes, the latter button press being a behavioral indication of the brain's excitability. In the forewarned reaction time task, patients developed a CNV with a frontal maximum, while the CNV in control subjects was predominantly centro-parietal. This atypical topographical pattern of the CNV may indicate a different spatio-temporal regulation of cortical preparatory processes in schizophrenics. Motor responses were accelerated during negative potential shifts in both patients and controls, with responses being slower overall in patients. In patients, probe-evoked potentials revealed a smaller N100, but a larger P300, than in controls. The covariation of these brain waves with slow potentials, however, turned out to be similar for both groups.

The magnetic counterpart of the contingent negative variation

The magnetic counterpart of the CNV, the contingent magnetic variation (CMV), was investigated in an Go/No Go design: subjects moved their index finger to the offset of a 4 sec tone of a certain frequency in the Go condition and were asked not to move during presentation of a 4 sec tone of different frequency in the No Go condition. During the preparatory interval, both the CMV and the electrical wave form followed a similar time course and both produced an equally pronounced statistical difference between conditions (Go and No Go). Compared to the variability in the auditory evoked fields, the CMV showed considerably more variance in the field distribution across subjects. The polarity reversal across the temporal surface of the head and the pronounced amplitudes over inferior temporal areas led us to conclude that a significant temporal activity contributes to both the late and the early CMV. However, neither for the early nor for the late CMV component did a single equivalent dipole prove to be a satisfying model. The data are consistent with the suggestion that the earlier as well as the later aspects of the CMV are fed through distributed sources in motoric, sensory and association areas, a distribution with considerable intersubject variability.