N2 P3 Research Articles

Flunitrazepam-induced changes in neurophysiological, behavioural, and subjective measures used to assess sedation

Introduction: Certain features of event-related potentials (ERPs), electroencephalographic (EEG), and behavioural measures vary with differing states of alertness and/or sedation. Purpose: This study was conducted to investigate changes in several measures usually viewed as reflecting states of sedation/sleepiness associated with the use of a range of doses of the hypnotic benzodiazepine (BZD) flunitrazepam (FNZ). Methods: This was a double blind, independent group design study of the effects of acute oral doses of FNZ in young healthy volunteers. Forty-eight subjects were randomly allocated to one of four groups—FNZ (0.6, 0.8, and 1.0 mg) and placebo (PLAC)—and tested prior to treatment and then in a posttreatment session close to the theoretical peak plasma concentration. ERP latencies and amplitudes were measured at midfrontal (Fz), midcentral (Cz), and midparietal (Pz) using a standard auditory oddball paradigm. EEG changes were assessed at Pz. Behavioural measures included the digit–symbol substitution test (DSST), a cancellation task (CT), and subjective ratings of alertness and attentiveness by the subjects (SUB) and the experimenter (EXP). Results: FNZ led to psychomotor impairments and decreased alertness and attention; these effects were consistent with previous findings. A progressive, dose-related increase in P3 latency occurred in Fz, Cz, and Pz, and there was an increase in N1 (Fz, Cz) and N2 (Fz). N2–P3 amplitude decreased in Fz. EEG power bands beta 1 increased for the two highest doses, but no significant differences were noted in theta, delta, and alpha bands. P3 latencies, experimenter-rated levels of alertness, and DSST scores differentiated all three doses of FNZ from PLAC. Conclusion: The most sensitive measures used were P3 latencies of the ERPs (which varied with FNZ dose), DSST, and the experimenter-rated levels of alertness. However, we found no evidence for the assumption that one single phenomenon was reflected in all measures and different mechanisms were probably involved. Further experiments will be needed for more in-depth probing of the finer mechanisms underlying sedation/sleepiness and how they affect behavioural and eletrophysiological measures of the central nervous system (CNS) function.

Topographic ERP changes due to displacements of visuo-spatial attention

In order to explore the cerebral processes of visuo-spatial attention shifts, the spatio-temporal characteristics of ERPs to targets following a spatial cue were examined topographically. Subjects were asked to respond selectively to a target presented 200 ms after offset of a spatial cue. Valid targets (75%) appeared at cue position; invalid targets (25%) were presented at a different position than the cue. In valid trials, an anterior negative deflection of Nd and a single-peaked P3 were observed with shorter reaction time. In invalid trials, a posterior N2–P3 complex was observed with delayed reaction time. Spatio-temporal patterns of brain electric fields (BEF) to valid and invalid trials differed between 240 and 280 ms after target presentation. Regardless of target locations, the BEF in valid trials was characterized by anterior negative/posterior positive distribution. On invalid trials, where subjects were forced to shift their visuo-spatial attention from the cue to the target, the BEF was characterized by an anterior positive/posterior negative distribution for all cue-target pairs except those presented in the upper visual field. Therefore, the BEF within 240–280 ms after the target presentation might be concerned with cerebral processes of visuo-spatial attention shift, i.e., with recapturing/evaluating target.

Facial expressions modulate the time course of long latency auditory brain potentials

Long latency auditory brain potentials were recorded while subjects listened to bi-syllabic words spoken with an emotional expression and concurrently viewed congruent or incongruent facial expressions. Analysis of the auditory waveforms suggests the existence of a positive deflection around 240 ms post-stimulus with a clear posterior topography (the P2b component). This potential is subsequent upon the modality-specific auditory N1–P2 components and precedes the amodal N2–P3 complex. Congruent face-voice trials elicited an earlier P2b component than incongruent trials suggesting that auditory processing is delayed in the presence of an incongruent facial context. These electrophysiological results are consistent with previous behavioural studies showing an acceleration of reaction times for rating voice expressions that are part of congruent bimodal stimulus pairs. A source localisation analysis performed on the scalp EEG during the time-window corresponding to the P2b component disclosed a single dipole solution in the anterior cingulate cortex.

Error-negativity and positivity as they relate to other ERP indices of attentional control and stimulus processing

We compared individual differences in the ERP associated with incorrect responses in a discrimination task with other ERP components associated with attentional control and stimulus discrimination (N2, P3, CNV). Trials with errors that are detected by the subject normally produce a negativity ( N E) immediately following the response followed by a positivity ( P E). The morphology of the N E and the P E is similar to that of the standard N2–P3 complex on correct discrimination trials. Our findings suggest that the P E is a P3 response to the internal detection of errors. The N E, however, appears to be distinct from the N2. Finally, even though both the contingent negative variation (CNV) and the N E are associated with prefrontal cortex and the allocation of attention to response accuracy, the N E and CNV did not relate to one another.

Brain event-related potentials (ERPs) in schizophrenia during a word recognition memory task

Impairments of recognition memory for words and attenuation of the ERP ‘old–new’ effect have been found in patients with left medial temporal lobe damage. If left temporal lobe dysfunction in schizophrenia involves medial structures (e.g. hippocampus), then schizophrenic patients might show similar abnormalities of verbal recognition memory. This study recorded ERPs from 30 electrode sites while subjects were engaged in a continuous word recognition memory task. Results are reported for 24 patients having a diagnosis of schizophrenia ( n=16) or schizoaffective disorder ( n=8) and 19 age-matched healthy controls. Both patients and controls showed the expected ‘old–new’ effect, with greater late positivity to correctly recognized old words at posterior sites, and there was also no significant difference between groups in P3 amplitude. However, accuracy of word recognition memory was poorer in patients than controls, and patients showed markedly smaller N2 amplitude. Reduced amplitudes of N2 and N2–P3 were associated with poorer performance, with highest correlations over the left inferior parietal (N2) and left medial parietal (N2–P3) region. Moreover, patients failed to show significantly greater left than right hemisphere amplitude of N2–P3 at posterior sites, which was seen for healthy controls. These findings suggest that impaired word recognition in schizophrenia may arise from a left lateralized deficit at an early stage of processing, beginning at 200–300 ms after word onset.

Event-related potential (ERP) asymmetries to emotional stimuli in a visual half-field paradigm.

To investigate the hypothesis of a right hemispheric superiority in negative emotional processing, event-related potentials (ERPs) were recorded from 17 sites (Fz, Cz, Pz, F3/4, F7/8, C3/4, T7/8, P3/4, P7/8, O1/2) in a visual half-field paradigm. While maintaining fixation, right-handed women viewed pictures of patients with dermatological diseases before (negative) and after (neutral) cosmetic surgery. A principal components analysis with Varimax rotation performed on ERPs revealed factors identified as N1, N2, early P3, late P3, and slow wave. Repeated measures analyses of variance performed on factor scores revealed a significant effect of emotional content for all factors except for N1. However, asymmetries in emotional processing were restricted to N2 and early P3, with maximal effects over the right parietal region. N2-P3 amplitude was augmented for negative and reduced for neutral stimuli over right hemisphere regions. Visual field presentation interacted with these asymmetries in enhancing amplitudes contralaterally for early but ipsilaterally for late ERP components. Overall, findings for N2 and P3 support theories of an asymmetry in emotional processing.

An ab initio and force field study on the conformation and chain flexibility of the dichlorophosphazene trimer

AbstractAb initio molecular orbital calculations have been used to study the conformation, valence electron charge density, and chain flexibility of a dichlorophosphazene trimer (CH3[NP(Cl2)]3CH3). The calculations were carried out at the restricted Hartree‐Fock level with the 6–31 G* basis set. The dichlorophosphazene trimer adopts a planar transcis conformation. The valence electron charge distribution indicates strong charge separations along the backbone of the molecule, and is in agreement with Dewar's island delocalization model for bonding in linear and cyclic phosphazenes. In order to determine the height of the torsional barrier (2,5 kcal/mol), the torsional potential of a central PN bond of the trimer was studied with a rigid rotor scan and geometry optimizations of selected rotamers. The flexibility of the PNP bond angle contributes significantly to the chain flexibility. Based on the results of the ab initio calculations, an empirical force field for the dichlorophosphazene trimer was developed. The energy expression includes bond stretch, angle bend, electrostatic, van der Waals, and torsional potential terms. A relaxed scan with the force field achieves good agreement with the ab initio results for the torsional potential in the vicinity of the stable conformation, and an excellent agreement with the ab initio results on changes in the P2N2P3 bond angle and the N1P2  N2P3 dihedral angle during a full rotation around the N2  P3 bond.

Empirical Rules on the Attenuation of Quasifree Scattering in Nucleon-Deuteron Breakup in the Energy Range from 15 to 156 MeV

Simple empirical rules are in existence on the (σ exp /σ s m ), the ratio of the experimental cross section for p-p and p-n quasifree scattering (QFS) to the one calculated with the spectator model. (1) The ratio for p-n QFS, (σ exp /σ s m ) p1–n2 , depends only on the relative energy E n2–p3 between scattered neutron and spectator proton, namely (σ exp /σ s m ) p1–n2 = f ( E n2–p3 ). (2) The ratio for p-p QFS, (σ exp /σ s m ) p1–n2 , depends on the relative energies E p1–n3 and E p2–n3 and is expressed by a product form of the same function for p-n QFS, namely (σ exp /σ s m ) p1–p2 = f ( E p1–n3 )× f ( E p2–n3 ). (3) Further, the function f ( E ) is expressed by the deuteron wave function in momentum space.

Auditory Evoked Potential in Stage 2 and REM Sleep During a 30‐Day Exposure to Tone Pulses

ABSTRACTTen subjects were exposed to 3.5K Hz tone pulses of 660 msec duration, presented 24‐hr‐per‐day for 30 days. The interstimulus interval was 22 sec. There were 10 days each at 80, 85, and 90 dB in that order. The average evoked potential (AEP) at C3 referenced to linked mastoids was obtained from contiguous stage 2 and REM sleep segments on the first, second, and last recorded nights of tone‐pulse exposure. The AEP was consistently larger in stage 2 than in REM sleep. In both stage 2 and REM sleep, AEP amplitude on the second recorded night bore no consistent relationship to first or last recorded night AEPs. Only the N2–P3 amplitude yielded consistent decreases, with 9 of 10 subjects in both stage 2 and REM sleep having smaller N2–P3 amplitudes on the last than on the first recorded night. There were no changes in latency of any component. During sleep there is little, if any, habituation of the auditory AEP during long‐duration exposures to nonmeaningful stimuli, and certainly no extinction of the AEP under these conditions.

GANIL: A Proposal for a National Heavy-Ion Laboratory

Under the control of the French Atomic Energy Commission (CEA) and of the National Institute of Nuclear and Particle Physics (I N2 P3) a multi accelerator system for heavy ions is beeing studied. The heart of this system consists of two identical conventionnal separated-sector cyclotrons K = 400 (SSC 1 and SSC 2); at the output of SSC 1 ions are stripped through a foil, high charge is selected and injected into SSC 2. The injection into SSC 1 will be achieved by a small compact cyclotron or by an 1 MV electrostatic accelerator. As the required beam must be intense and precise (energy resolution and emittance) special attention has been paid for a careful matching of the three stages of acceleration in transversal and longitudinal planes taking into account space charge forces as well as electric and magnetic defects. A set of parameters for the two main machines and their injectors is given.