Policosanol, reaction time and event-related potentials

The aim of the present study was to compare the results of a 1-week, double-blind placebo-controlled trial investigating the effects of isopolicosanol and octacosanol on reactivity and related brain activity. In particular, reaction time (RT) and event-related potentials such as contingent negative variations (CNV) and P300 (P3) have been studied. Thirty sedentary healthy students were tested before and after treatment (3.6 mg/die for 7 days) with orally administered tablets of placebo (group A), isopolicosanol (B) and octacosanol (C). RT were studied according to three procedures: simple RT (SRT), go/no-go RT (GRT) and choice RT (CRT). Results show that before treatment, there were no significant differences between groups A, B and C. After treatment, the RT of group A was unchanged, while the RT of groups B and C were reduced. In group B, in the SRT test, the reduction of RT was accompanied by electrical data exhibiting increased amplitudes of CNV and shorter latencies of P3. These results show that the main effect on reactivity and event-related potentials can be ascribed to policosanol and is mainly evident in the SRT test.     

Time course of corticospinal excitability in reaction time and self-paced movements

We used transcranial magnetic stimulation (TMS) to study the time course of corticospinal excitability before and after brisk thumb abduction movements, either in a simple reaction time (RT) paradigm or self-paced. Premovement increase in corticospinal excitability began about 20 msec earlier for self-paced compared with simple RT movements. For both simple RT and self-paced movements after electromyographic (EMG) offset, there was a first period of increased excitability from 0 to 100 msec, followed by a second period from 100 to 160 msec. Corticospinal excitability was decreased from about 500 to 1,000 msec after EMG offset for both types of movements. Our results show that motor preparation that begins 1.5 to 2 seconds before self-paced movement is not associated with increased corticospinal excitability. The first phase of increased corticospinal excitability after EMG offset may be due to activity of motor cortex neuron subthreshold for activating spinal motor neurons, and the second phase may reflect a subthreshold second agonist burst. The period of decreased corticospinal excitability after movement corresponds to the onset of event-related synchronization (ERS) of electroencephalographic signals in the 20-Hz band, and supports the hypothesis that ERS may be related to an inactive, idling state of the motor cortex.     

Lateralization of event-related beta desynchronization in the EEG during pre-cued reaction time tasks.

OBJECTIVE: Here, we investigate whether the event-related desynchronization (ERD) of spectral components of the cortical EEG in the beta (13-30 Hz) frequency range may, in part, index motor selection processes. Specifically, we sought evidence for a contralaterally dominant component of the beta ERD that is limited to trials in which motor selection is possible prior to any imperative cue to move, with attendant behavioural advantage. METHODS: We measured reaction time and assessed the lateralization of beta ERD in 12 healthy volunteers as they performed pre-cued choice reaction time tasks, in which warning S1 cues were either fully predictive about the laterality of a subsequent imperative S2 signal or provided no laterality information. We calculated 'lateralized ERD index' (LERDI), a parallel measure to the lateralized readiness potential in the time domain. RESULTS: Trials with 100% S1-S2 congruency produced significantly shorter reaction times than trials with 50% S1-S2 congruency, where laterality information was unreliable. Beta LERDI indicated significantly greater lateralisation of the ERD in the warning-go interval and of event-related synchronization (ERS) following movement in the 100% condition than in the 50% condition. The lateralization of the beta ERD with respect to hand persisted, even when subjects were instructed to make movements of opposite laterality to those prompted. CONCLUSIONS: Lateralized EEG changes occur in the beta band in the S1-S2 interval prior to movement, but only when informative warning cues allow early motor selection, as suggested by the shortening of reaction time. Furthermore, the enhanced contralateral ERS with 100% S1-S2 congruency suggests that this phenomenon is at least partly independent of afferent feedback, as the same movement was made in the 100 and 50% conditions. SIGNIFICANCE: Lateralized suppression of beta power prior to externally generated movements is associated with motor selection.     

On the time resolution of event-related desynchronization: a simulation study.

OBJECTIVES: To investigate the time resolution of different methods for the computation of event-related desynchronization/synchronization (ERD/ERS), including one based on Hilbert transform. METHODS: In order to better understand the time resolution of ERD/ERS, which is a function of factors such as the exact computation method, the frequency under study, the number of trials, and the sampling frequency, we simulated sudden changes in oscillation amplitude as well as very short and closely spaced events. RESULTS: Hilbert-based ERD yields very similar results to ERD integrated over predefined time intervals (block ERD), if the block length is half the period length of the studied frequency. ERD predicts the onset of a change in oscillation amplitude with an error margin of only 10-30 ms. On the other hand, the time the ERD response needs to climb to its full height after a sudden change in oscillation amplitude is quite long, i.e. between 200 and 500 ms. With respect to sensitivity to short oscillatory events, the ratio between sampling frequency and electroencephalographic frequency band plays a major role. CONCLUSIONS: (1) The optimal time interval for the computation of block ERD is half a period of the frequency under investigation. (2) Due to the slow impulse response, amplitude effects in the ERD may in reality be caused by duration differences. (3) Although ERD based on the Hilbert transform does not yield any significant advantages over classical ERD in terms of time resolution, it has some important practical advantages.     

Simple reaction time event-related potentials: Effects of alcohol and diazepam

1. 1. Acute effects of alcohol and diazepam on reaction time (RT) and event-related potential (ERP) measures were examined in 108 healthy male volunteers.

2. 2. The subjects engaged in a simple RT task at two levels of stimulus intensity during baseline and treatment sessions.

3. 3. Lower stimulus intensity produced increased RTs, increased ERP peak latencies, and suppression of peak amplitudes.

4. 4. Moderate and high doses of alcohol, and high doses of diazepam produced increased RTs. Alcohol suppressed P100 and N100 amplitudes, while diazepam suppressed P100 amplitudes only. P100 amplitudes were correlated to RTs under baseline and treatment conditions.

5. 5. These results were taken as evidence for impaired stimulus detection during alcohol and diazepam intoxication, with both drugs influencing sensory-perceptual processes and alcohol alone influencing the degree of attentiveness.

Event-related slow potentials in rat cortex during a reaction time task: Cortical area differences

Event-related slow potentials were recorded from frontal and visual cortex of rats during a reaction time task in which trials were initiated at variable intervals by an auditory warning stimulus. Transcortical slow potential (SP) responses during the two-second period between onset of the warning stimulus and extension of a retractable lever were analyzed, using single trial and averaged response data. SP responses recorded from the two cortical areas differed significantly with respect to waveform and amplitude. The results indicate that event-related slow potentials from rat cortex are area dependent and that the small size of the rat brain does not preclude recording of SP changes with differential cortical distribution.     

Event-related desynchronization and excitability of the ipsilateral motor cortex during simple self-paced finger movements.

OBJECTIVE: To study the time course of oscillatory EEG activity and corticospinal excitability of the ipsilateral primary motor cortex (iM1) during self-paced phasic extension movements of fingers II-V. METHODS: We designed an experiment in which cortical activation, measured by spectral-power analysis of 28-channel EEG, and cortical excitability, measured by transcranial magnetic stimulation (TMS), were assessed during phasic self-paced extensions of the right fingers II-V in 28 right-handed subjects. TMS was delivered to iM1 0-1500 ms after movement onset. RESULTS: Ipsilateral event-related desynchronization (ERD) during finger movement was paralleled by increased cortical excitability of iM1 from 0-200 ms after movement onset and by increased intracortical facilitation (ICF) without changes in intracortical inhibition (ICI) or peripheral measures (F waves). TMS during periods of post-movement event-related synchronization (ERS) revealed no significant changes in cortical excitability in iM1. CONCLUSIONS: Our findings indicate that motor cortical ERD ipsilateral to the movement is associated with increased corticospinal excitability, while ERS is coupled with its removal. These data are compatible with the concept that iM1 contributes actively to motor control. No evidence for inhibitory modulation of iM1 was detected in association with self-paced phasic finger movements. SIGNIFICANCE: Understanding the physiological role of iM1 in motor control.     

Effects of target area and letter complexity on event-related potentials and reaction time.

The idea that an area of the visual field stimulated by a recognizable image activates a corresponding area of neural tissue that generates the recognition potential (RP) was examined. Sixteen subjects detected targets in a stream of non letter character arrays. The targets were one or five rows of a repeated letter (O or G). RT was less for the larger targets and less for O than for G. RP latency differences agreed with the RT differences. RP amplitude was substantially greater for large than for small targets and moderately larger for G than for O. P3 amplitude showed a different relationship. The observed amplitude-latency relationships indicated that differences in stimulus strength were not responsible for the greater RP evoked by the larger targets. The results strengthened the neural area explanation for RP amplitude modulation by the area of the visual fields impinged on by recognizable images.     

Effects of caffeine on event-related potentials: Comparison of oddball with single-tone paradigms

We investigated the acute effects of caffeine (500 mg) on event-related potentials (ERP) in 10 healthy subjects using standard oddball and single-tone paradigms. Event-related potentials were recorded before oral ingestion of caffeine or placebo and 30 min and 210 min after. The oddball paradigm, but not the single-tone paradigm, showed that the P300 amplitude and the area were significantly increased 30 min after ingestion of caffeine and significantly decreased 30 min after ingestion of placebo. The effects of caffeine disappeared at 210 min. Neither the P300 latency nor the reaction time changed significantly with the oddball paradigm. However, the reaction time was shortened 30 min after ingestion of caffeine with the single-tone paradigm. These findings suggest that the caffeine-induced increase in the P300 amplitude may have resulted from the increased allocation of attentional resources to the discriminating process which was not, however, accompanied by facilitation of the process and that caffeine may specifically stimulate the discriminating process involved in the oddball paradigm. In addition, the simple psychomotor performance of button-pressing in response to a tone signal was accelerated by caffeine.     

Event-related potentials during auditory oddball, and combined auditory oddball-visual paradigms

The purpose of the current study was to investigate the properties of a new modification of the classical auditory oddball paradigm (auditory oddball paradigm combined with passive visual stimulation, AERPs + VEPs) and compare the scalp topography obtained with the new paradigm and the classical auditory oddball paradigm (AERPs) in healthy humans. The responses to bimodal stimulation, and to the classical oddball paradigm were similar to those reported in other studies in terms of location, amplitudes, and latencies of P1, N1, P2, N2, and P300. The new modification of the oddball paradigm produced P300 at fronto-central locations in contrast to centro-parietal locations during the classical oddball paradigm. The amplitudes and latencies of P300 were also significantly larger during the new than the classical paradigm. Furthermore, the amplitudes of N1 and P2, but not N2 were significantly higher and differed in location during the new paradigm in response to both target and standard stimuli. The latencies of all three waves were significantly longer and the latency of P2 differed in location between the new and the classical paradigms in response to only the standard stimuli. The results of this study suggest that the new modification of the classical oddball paradigm produces different neural responses to the classical oddball paradigm. Therefore, this modification can be used to investigate dysfunctions in sensory and cognitive processing in clinical samples.     

New measures to detect malingered neurocognitive deficit: applying reaction time and event-related potentials

The ability of the Test of Memory Malingering (TOMM), reaction times (RTs), and event-related potentials (ERPs) to detect malingered neurocognitive deficit (MNCD) was examined in 32 normal individuals answering under honest (HON; n = 16) or malingering (MAL; n = 16) instructions as well as in 15 patients with traumatic brain injury (TBI) who answered under honest instructions. Overall, the TOMM was the most effective at classifying groups. However, new accuracy, RT, and ERP measures reached promising hit rates in the range of 71-88%. In particular, the difference in frontal versus posterior ERP obtained during an old-new task was effective at classifying MAL versus TBI (hit rate = 87%).     

Event-related desynchronization: the effects of energetic and computational demands.

The effects of a subject's activation state on cognitive processing were studied, while subjects performed verbal and non-verbal tasks under a speed and accuracy instruction. It was found that stressing speed influenced the level of prestimulus alpha power and consequently the amount of relative event-related desynchronization (ERD). Increasing task complexity led to an increase in the amount and duration of relative ERD. Both prestimulus level of alpha power and relative ERD were asymmetrically distributed over the left and right hemispheres. No verbal/non-verbal task-dependent asymmetries in phasic ERD were found. The data suggest that the level of prestimulus alpha power is mainly influenced by the subject's activation state, whereas relative ERD mainly reflects phasic changes in cognitive processing.     

Event-related EEG/MEG synchronization and desynchronization: basic principles.

An internally or externally paced event results not only in the generation of an event-related potential (ERP) but also in a change in the ongoing EEG/MEG in form of an event-related desynchronization (ERD) or event-related synchronization (ERS). The ERP on the one side and the ERD/ERS on the other side are different responses of neuronal structures in the brain. While the former is phase-locked, the latter is not phase-locked to the event. The most important difference between both phenomena is that the ERD/ERS is highly frequency band-specific, whereby either the same or different locations on the scalp can display ERD and ERS simultaneously. Quantification of ERD/ERS in time and space is demonstrated on data from a number of movement experiments.     

The paradoxical effect of warning on reaction time: Demonstrating proactive response inhibition with event-related potentials

ObjectiveWarning signals can induce a paradoxical increase in reaction time (RT) when detecting targets. Top-down inhibitory control intended to prevent undesired responses to non-target stimuli may account for this effect. This hypothesis assumes the existence of a gating mechanism during conditions of uncertainty that locks the initiation of movement before any stimulus is presented and thus increases the RT to any targets that are not preceded by warning cues. However, direct evidence for the involvement of inhibitory mechanisms in the paradoxical warning effect is still lacking.MethodsEvent-related potentials (ERPs) were analyzed by means of a target detection task according to two experimental protocols: one requiring inhibition (warned and unwarned trials mixed in the same block) and the other not requiring inhibition (warned and unwarned trials separated into different blocks).ResultsThe probability that warning signals would be introduced in a block (mixed-block design) dramatically increased RT to unwarned targets and evoked target-locked markers of inhibition in these trials (N2 was evoked and P3 was delayed). Cue-locked ERPs also exhibited a strong N2 component whatever the design.ConclusionsThe top-down control implemented in the pre-stimulus period to prevent undesired automatic responses to external events inhibits the triggering of movement.SignificanceUnderstanding this gating mechanism may provide insight into various neurological or psychiatric disorders affecting movement initiation, such as akinesia or impulsivity that may both be viewed as disorders of higher order inhibitory control.     

Event-related desynchronization and synchronization during a memory task in children

OBJECTIVE: To examine the event-related desynchronization (ERD) and synchronization (ERS) responses of several narrow electroencephalographic (EEG) frequency bands in children during an auditory memory task. METHODS: ERD/ERS responses of the 4-6, 6-8, 8-10 and 10-12 Hz EEG frequency bands were studied in 12 children (mean age 12 years) while they performed an auditory memory task. Twelve adult subjects served as a control group. RESULTS: The children's ERD/ERS responses differed from those of the adult's in the 4-6, 6-8 and 8-10 Hz EEG frequency bands, especially during retrieval from memory. The children's 4-6 Hz initial ERS responses were of lesser amplitude and of delayed latency as compared to those of the adults. In the 6-8 and 8-10 Hz frequency bands, especially during retrieval from memory, the children's ERD responses were of lesser magnitude than those of the adults. In the 10-12 Hz frequency band, no differences were observed between the ERD/ERS responses between the children and adults. CONCLUSIONS: Our results suggest that theta and alpha response systems might participate in auditory information processing already at this age, although not being fully developed. Memory systems involving retrieval may be the last to mature.     

Mapping of event-related potentials to auditory and visual odd-ball paradigms in controls

The paper reports the results of recordings and maps of event-related potentials (ERPs) obtained in normal subjects. ERPs were recorded from 19 scalp electrode derivations using both visual and acoustic paradigms. In normal subjects, topographical distribution of all ERP components is described in detail. Our findings in normals suggest that the early modulation of stimulus-related potentials could be located in primary associative areas, and that N2, P3a, P3b, and SW have different distributions.     

Effects of stimulus sequence on event-related potentials and reaction time during target detection in Alzheimer's disease.

OBJECTIVES: To examine evoked potentials and behavior as a function of stimulus sequence in an auditory target detection paradigm in Alzheimer's disease (AD). METHODS: Evoked potentials and reaction times were collected from 12 healthy elderly controls and 10 patients with mild AD. Subjects pressed a response button to high-pitched target tones (P=0.20) that were randomly intermixed with low-pitched frequent tones. We measured pre-stimulus readiness potential (RP), event-related potentials (P50, N100, P200, N200 and P300), and reaction time as a function of the stimulus sequence. RESULTS: AD subjects performed at comparable levels of accuracy as controls, but had significantly increased reaction times. Grand averaged potentials in AD showed a significant reduction of the amplitude of the RP, and an increase of P300 latency. Both controls and AD showed speeding of reaction time, increases in RP amplitude, and decreases in P300 latency as a function of the number of frequents preceding the target. Sequential changes of other components (P200 and N200) were found in controls but not AD. CONCLUSIONS: AD patients have systematic changes of both RT and certain of the evoked potential components as a function of stimulus sequence. Moment-by-moment changes in target expectancy are largely preserved in AD, even though overall performance and evoked potential measures of expectancy (RP) and stimulus classification (P300 latency) are abnormal.     

Event-related potentials in psychiatry.

Electrophysiological assessments of psychiatric disorders have produced a number of promising, highly replicable findings and thus carry the potential of becoming clinically utilizable in the diagnostic or prognostic evaluation of psychopathological conditions. The procedures involved are rather complex technically and the interpretation of the findings require a combined neurophysiological and clinical expertise. On the other hand, electrophysiological techniques are in general non-invasive and relatively inexpensive, and neurophysiology laboratories are widely available in the clinical setting. Among these techniques, event-related potentials (ERPs) are of major interest in psychiatry, particularly since these tools can indicate cortical neuronal dysfunctions, which play a major role in various neuropsychiatric disorders.