Working memory dysfunction in major depression: an event-related potential study.

OBJECTIVES: To study working memory function in untreated major depression using a digit probe identification and matching task. Methods: We compared behavioural performance and event-related potentials during processing of the Sternberg working memory task in 14 depressed patients and 14 healthy matched control subjects. RESULTS: Patients made more mistakes than controls as the memory load was increased from one to 5 digits and had significantly slower reaction times at all levels of memory load. The patients' event-related potentials (ERPs) differed significantly from controls. Pathological changes were similar for auditory and visual presentation. Surface negative activity in the 157-210 ms section of the waveform was reduced for all levels of memory load, suggesting abnormal sensory/perceptual processing in the modality-specific association cortices, possibly due to a failure of selective attention mechanisms. In the 375-840 ms epoch, the patients' responses showed large amplitude sustained negative activity, maximal at Cz and a reduced late positive wave. The large prolonged negativity in the patients' ERPs suggests activation of additional neuronal assemblies than those normally participating in the task. This could reflect either compensatory mechanism or dysfunction of inhibitory systems. These changes were sensitive to memory load, suggesting that they reflect alterations of memory-related processes. CONCLUSIONS: This study provides objective evidence that major depression significantly affects working memory. The ERP changes in depression could be accounted for by dysfunction of the central executive control of working memory.     

Neural effects of nicotine during auditory selective attention in smokers: an event-related potential study

Acute nicotine has been found to improve task performance in smokers after smoking abstinence, but the attentional processes mediating these improvements are unclear. Since scalp-recorded event-related potentials (ERPs) have been shown to be sensitive indicators of selective attention, the effects of acutely administered nicotine were examined on ERPs and concomitant behavioural performance measures in an auditory selective attention task. Ten (6 males) overnight smoking-abstinent cigarette smokers received nicotine gum (4 mg) in a randomized, double-blind, placebo-controlled, crossover design. In a dichotic listening task [which required participants to attend and detect (target) deviant stimuli in one ear and to ignore similar stimuli in the other ear] which included ERP recordings and assessment of response speed and accuracy measures, nicotine gum failed to alter behavioural performance or amplitudes of ERP components sensitive to selective attention [reflected in the N100 and negative difference (Nd) component] or to pre-attentive detection of acoustic change [reflected in the mismatch negativity (MMN) component]. However, nicotine did influence the speed of these voluntary selective processes, as reflected by shortened latencies of the early Nd component. The findings are discussed in relation to the stimulus filter theory of smoking, and with respect to nicotine's actions on involuntary and controlled aspects of selective attention processes.     

Event-related brain potentials in reading disabled children during an inverse serial digit detection task.

It has been reported that limitations in different components of working memory could underlie reading disabilities. In addition, reading-disabled (RD) children seem to perform worse when digit name processing is required. With the purpose to explore further these assumptions one inverse serial digit detection task was evaluated using event-related brain potentials in fifteen 8-year-old RD children and a control group (CG). CG obtained significantly more correct responses than RD, but had similar reaction times. The experimental task performance significantly correlated with the performance on reading tests. Difference event-related potentials showed a voltage component peaking at 160 ms over frontocentral leads (P160d) that reached significantly higher amplitude in RD group, and was interpreted as an index of the amount of neural resources involved in visual working memory load. The amplitude of P160d significantly correlated with reading speed, the backward digit span and with the experimental task performance. Present results point out that highly demanding working memory tasks reveal behavioral and electrophysiological differences in RD children with respect to healthy controls.     

Sequential information processing during a mental arithmetic is reflected in the time course of event-related brain potentials.

OBJECTIVE: We hypothesized that mental arithmetic is a complex of sequential information processing. In order to test the hypothesis, event-related potentials (ERPs) were measured during 3 mental tasks. METHODS: Fifteen normal human subjects performed the following tasks; (1) subjects added up every digit delivered successively on a computer display, (2) subjects counted the number of presented digits, or (3) subjects counted the number of meaningless patterns. Spatiotemporal differences between ERP waveforms under the 3 tasks were studied within the period of 1200 ms post-stimulus. RESULTS: During the adding task, N120-P180-N220 complex advanced in latency in the left frontal, central and parietal regions. P300 increased in amplitude in the frontal and temporal regions during adding and counting digits, which was specific to the digit presentation. A positive slow potential depended on the adding task and showed two spatiotemporal distributions; one was a widespread brain activity over the frontal, central, temporal and parietal regions observed within 400-820 ms, and another was a brain activity restricted to the frontal region lasting up to 1150 ms. CONCLUSIONS: The results suggest that the early portion of ERPs reflects identification of physical attributes of stimuli and numeric meaning of digits, and that the positive slow potential reflects processes associated with calculation.     

Effects of visual attentional load on auditory processing

Auditory evoked potentials were recorded while participants attended to visually presented digits. The difficulty of the visual task was manipulated by requiring participants to process only the current digit (0-back) or both the current and the preceding digit (1-back). Tones deviating in frequency from standard tones elicited a frontal mismatch negativity peaking around 200 ms which did not vary with visual task. However, decreasing the visual task load enhanced a right-temporal positive wave peaking around 200 ms when tones were presented slowly, and a frontocentral negative wave peaking around 450 ms when tones were presented more rapidly. The degree to which task-irrelevant sounds are processed therefore depends on the degree to which a visual task engages attentional resources.     

Late sequelae of a non-optimal neonatal neurological condition in ERPs at the age of 11-13 years

In a longitudinal study a selective attention task was administered to 11-13-year-old children. During this task (employing a combined filter and selective-set paradigm), event-related brain potentials were recorded to study timing and morphology of early and late selection processes. Task performance was prospectively and retrospectively related to neurological optimality at birth and to flash-evoked potential correlates that were registered at the age of five. The results provided evidence that even after 13 years neonatal neurological suboptimality was reflected in task performance, both in reaction time and in electrophysiological data. Task load interacted with group classification according to optimality to the disadvantage of suboptimals. This implied that load demands differentiated between groups. The event-related brain potentials revealed the existence of a negative shift associated with memory load (search-related negativity) at Fz and Cz, and a positive deflection at Pz (P3b) associated with target detection. Cortical activity, expressed in terms of these deflections, appeared to be less pronounced for the suboptimal group.     

The relation between event related potential and working memory in healthy subjects

In numerous investigations the P300-component of the event related potential has proved a valid indicator of memory activities. The present study explores the amplitude and latency of the components of event-related potential regarding short-term memory task. Event related potentials, elicited by auditory stimuli, were recorded in 40 healthy subjects. For evaluating short term memory capacity of a subject, software in Delphi for Windows language was written. Algorithm of the software was the presentation of randomly selected four different digits for 4 seconds, removing it and waiting for subject's response, adding one digit, if response was true, otherwise decreased by one. After 20 trials, mean of recall time for true answers was computed. The subjects with high recall time showed prolonged latency of P300. A positive correlation was found between P300 latency and recall time. No correlation was found between N1, P2 and N2 latency or amplitude and recall time. These results suggest that memory problems are well correlated with the abnormalities of P300.     

The contingent negative variation during a memory retrieval task.

Evoked potentials were recorded from the human scalp during performance of a memory retrieval task modeled after a paradigm originated by Sternberg (1966). Subjects were required to decide whether a probe digit was contained in a series of one to four target digits presented a few seconds before. The amplitude of the contingent negative variation (CNV) preceding the probe digit and the speed of CNV resolution after the probe varied as a function of target set size. CNV amplitude was greatest when the set size was one. The smaller the set size, the more positive the evoked potential 300 msec after the probe, regardless of whether a motor response was required.     

Danger is worse when it moves: neural and behavioral indices of enhanced attentional capture by dynamic threatening stimuli

Both dynamic non-emotional stimuli (moving dots or digits) and danger-related static stimuli have previously shown to capture attention. This study explored whether the combination of the two factors (i.e., threatening moving stimuli), frequent in natural situations, enhances attentional capture. To this end, static and moving distractors containing emotionally negative and non-negative information were presented to 30 volunteers while they were engaged in a digit categorization task. Behavioral responses and event-related potentials (ERPs) were analyzed. Behavioral and electrophysiological data were convergent: moving negative distractors produced the longest reaction times in the digit categorization task, and elicited the highest amplitudes in the P1 component of the ERPs (peaking at 112ms), an electrophysiological signal of attentional capture. These results suggest that motion provides additional salience to threatening stimuli that facilitates attentional capture.     

Linking performance with brain potentials: mental rotation-related negativity revisited

It has been suggested that the amplitude of parietal event-related potentials (ERPs) provides a neural signature of imaginary object rotation. Here, we evaluated the relationship between the so-called rotation-related negativity and individual performance in the mental rotation of alphanumeric characters. The signals were averaged with respect to two time events, stimulus onset (ERP(ONSET)) and response time (ERP(RT)) indexing, respectively, an early and a late phase of the mental rotation. The amplitude of a slow parietal negativity varied with the rotation angle in both ERP(ONSET) and ERP(RT). The amplitude of this potential correlated negatively with task performance, indexed by response time. This was the case in ERP(RT) but not in ERP(ONSET). We further show that variations of the ERP(ONSET) amplitude with the rotation angle might at least partially result from increased duration/latency jitter among single trials. These results suggest that late rather than early processing supports task solution in mental rotation.     

Repetitive transcranial magnetic stimulation over the right dorsolateral prefrontal cortex disrupts digit span task performance

The digit span task measures the maintenance of information in short-term memory, and is one of the most widely used tests in clinical and experimental neuropsychology. Functional imaging studies have suggested a role of the right dorsolateral prefrontal cortex (DLPFC) in digit span performance. It remains unclear however, whether activation of this area is critical for task performance. Using repetitive transcranial magnetic stimulation (rTMS) over the right DLPFC in a sham-controlled design, we tested the hypothesis of the involvement of the right DLPFC in digit span task performance. We observed a significant disruption of digit span performance in healthy subjects in the real rTMS condition as compared to the sham condition. This effect of rTMS did not differ between digits forward and digits backward. Our results suggest that the right DLPFC is critical for central executive processes utilized by the digits forward and backward tasks.     

Top-down and bottom-up visual information processing of non-social stimuli in high-functioning autism spectrum disorder

Individuals with high-functioning autism spectrum disorder (HF-ASD) often show superior performance in simple visual tasks, despite difficulties in the perception of socially important information such as facial expression. The neural basis of visual perception abnormalities associated with HF-ASD is currently unclear. We sought to elucidate the functioning of bottom-up and top-down visual information processing in HF-ASD using event-related potentials (ERPs). Eleven adults with HF-ASD and 11 age-matched normal controls (NC) participated in this study. Visual ERPs were recorded using 128-channel EEG. The P1 and P300 were recorded in response to target stimuli. Visual mismatch negativity (vMMN) potentials were obtained by subtracting responses to standard from those to deviant stimuli. Behaviorally, individuals with HF-ASD showed faster target detection than NCs. However, vMMN amplitude and latency were the same between the two groups. In contrast, P1 and P300 amplitudes were significantly decreased in HF-ASD compared with NCs. In addition, P300 latency was significantly delayed in HF-ASD. Individuals with HF-ASD exhibit altered visual information processing. Intact bottom-up attention (vMMN) may contribute to their superior simple visual task performance in spite of abnormal low-level (P1) and top-down (P300) visual information processing.     

Effect of mild head injury on event-related potential correlates of Stroop task performance.

The effect of mild head injury on event-related potential (ERP) correlates of Stroop task performance was explored with the aim of further elucidating the basis of processing impairments after mild head injury. Computer- and card-based Stroop tasks were employed to assess attention function. A sequence of incongruent color words were presented followed by a sequence of congruent color words (printed in congruent colors). Control performance was equivalent on computer- and card-based versions of the incongruent task and faster on the congruent card task than the preceding congruent computer task. The mild head injury group were as fast as controls on the computer-based task but made more errors. However, they were relatively slower on both the congruent and incongruent parts of the card-based task and made more errors in the incongruent task. ERP correlates of computer-based Stroop task performance suggested a greater allocation of attention resources in the incongruent condition in both groups in the form of relatively greater negativity in the latency range 350 to 450 ms with a distribution consistent with the activation of the anterior cingulate gyrus. In addition the mild head injured group showed relatively greater enhancement than the control group in this latency range in both congruent and incongruent conditions. There was, however no evidence of reduced amplitude P1, N1, N2, or P3b deflections. Trails, digit symbol, digit span and auditory verbal learning tests (AVLT) were also administered. Mild head injured participants were impaired only on the AVLT. The finding of greater ERP negativity in the mild head injured group is consistent with greater allocation of attention resources to achieve equivalent performance in the computer-based Stroop task.     

Inhibition control impairments in adolescent smokers: electrophysiological evidence from a Go/NoGo study

Smoking during adolescence may promote nicotine dependence later on in life. Therefore, it is extremely important to study the neural mechanisms of adolescent smokers. As inhibition control is emphasized in several contemporary theoretical models of addiction, in the current study, we focused on the electrophysiological evidence of inhibition control deficits in adolescent smokers. By using relatively homogenous groups of adolescent smokers (n = 18) and matched nonsmokers (n = 18), we employed event-related potentials (ERP) to investigate the N200 and P300 amplitude and latency differences during a Go/NoGo task between the adolescent smokers and nonsmokers. Relative to nonsmokers, more NoGo response errors, reduced NoGo P300 amplitude, and longer P300 latency were observed in adolescent smokers. Correlation analysis revealed that the NoGo P300 amplitudes were significantly correlated with NoGo errors in both adolescent smokers and nonsmokers. Our findings provided direct electrophysiological evidence for inhibitory control impairments in adolescent smokers. It is hoped that our results may enhance understanding of the pathology of inhibitory control in adolescent smokers.     

Endogenous event-related potentials in obsessive-compulsive disorder

Brain event-related potentials (ERPs) were used to investigate central nervous system (CNS) correlates of cognitive function in obsessive-compulsive disorder (OCD). ERPs of 10 unmedicated OCD patients and 10 normal controls were measured in an auditory "oddball" task. Increasing task difficulty resulted in longer N200 and P300 latencies in normal subjects, but not in OCD patients. Moreover, OCD patients displayed shorter P300 latency than normal controls for the more difficult discrimination conditions. This replicates prior findings of Beech et al. (1983) for a visual task. For both levels of task difficulty, OCD patients also showed greater negativity than normal controls in the N200 region, which extended into the subsequent slow wave region. Negativities in the N200 and slow wave regions were larger at sites over the left hemisphere than the right hemisphere. The enhanced negativities and reduced P300 latency in OCD patients are discussed in terms of current theories postulating cortical hyperarousal and left hemisphere involvement in OCD.     

Serial position effects in auditory event-related potentials during working memory retrieval

It is established that recall of an item from a list of sequentially presented items is sensitive to the item's position in the memorized list. However, little is known about the brain mechanisms that mediate these serial position effects. Studies of working memory retrieval using event-related potentials report amplitude reductions during retrieval (auditory cortical N100, neocortical late positive wave [LPW]) as memory load increases. We tested the hypothesis that N100 and LPW amplitudes to probes are also affected by serial position. Event-related potentials were recorded from subjects performing an auditory working memory task. A set of one or five digits was memorized, then subjects classified a probe digit as either present or absent from the memory set. A control task was also given. Amplitudes of the N100 and LPW were reduced in the 5-item versus the 1-item set. In the 5-item set N100 amplitude was significantly larger for the initial (1st) serial position, relative to Positions 2-5, while linear increases in LPW amplitude were seen across serial positions (5th > 1st position). A control task without memorization showed no N100 or LPW amplitude changes with set size or serial position. The findings reveal that the N100 and LPW are influenced differently by serial position during working memory retrieval: N100 shows a primacy effect and LPW demonstrates a recency effect. The results suggest that primacy and recency effects may be mediated by different brain regions at different times during memory retrieval.     

Superior digit memory of abacus experts: an event-related functional MRI study

Abacus experts exhibit superior short-term memory for digits, but the underlying neurophysiological mechanism remains unknown. Using event-related fMRI, we examined the brain activity of abacus experts and non-experts during the memory retention period of a delayed match-to-sample task using digits as stimuli. In controls, activity was greater in cortical areas related to verbal working memory, including Broca's area. In contrast, in experts, activity was greater in cortical areas related to visuo-spatial working memory, including the bilateral superior frontal sulcus and superior parietal lobule. This provides neurophysiological evidence that abacus experts utilize a visuo-spatial representation for digit memory.     

Brain indices of music processing: "nonmusicians" are musical

Only little systematic research has examined event-related brain potentials (ERPs) elicited by the cognitive processing of music. The present study investigated how music processing is influenced by a preceding musical context, affected by the task relevance of unexpected chords, and influenced by the degree and the probability of violation. Four experiments were conducted in which "nonmusicians" listened to chord sequences, which infrequently contained a chord violating the sound expectancy of listeners. Integration of in-key chords into the musical context was reflected as a late negative-frontal deflection in the ERPs. This negative deflection declined towards the end of a chord sequence, reflecting normal buildup of musical context. Brain waves elicited by chords with unexpected notes revealed two ERP effects: an early right-hemispheric preponderant-anterior negativity, which was taken to reflect the violation of sound expectancy; and a late bilateral-frontal negativity. The late negativity was larger compared to in-key chords and taken to reflect the higher degree of integration needed for unexpected chords. The early right-anterior negativity (ERAN) was unaffected by the task relevance of unexpected chords. The amplitudes of both early and late negativities were found to be sensitive to the degree of musical expectancy induced by the preceding harmonic context, and to the probability for deviant acoustic events. The employed experimental design opens a new field for the investigation of music processing. Results strengthen the hypothesis of an implicit musical ability of the human brain.     

Event-related potential (ERP) correlates of performance of intelligence tests.

Any relationship between measures of cognitive function and brain electrical activity would be of considerable importance in the objective assessment of patients suspected of intellectual impairment. In healthy subjects, we have found a strong correlation between the event-related potentials evoked by a digit probe identification task and scores on intelligence tests (WAIS). Responses from subjects with higher performance on IQ tests are significantly 'more negative' than those from subjects with lower IQ. The characteristics of these IQ-dependent electrophysiological features suggest that they may be related to the subject's ability to focus on a task.     

Left ear performance in dichotic listening following commissurotomy

Contribution of the left ear stimulus to dichotic listening performance following commissurotomy was studied in five patients. In two tasks, subjects were asked to identify in writing both members of a pair of competing stimuli, either digits or CV syllables. A third task required subjects to integrate high and low frequency components of a single word presented dichotically. Left ear performance was at chance level for CV syllables but exceeded 80% for four out of five patients on the digit stimuli. All patients showed evidence of being able to utilize left ear information in the dichotic fusion task. Results indicate that apparent supression of left ear material in the dichotic task is a function of spectral-temporal overlap between competing stimuli.