Multi-feature mismatch negativity: How can reliable data be recorded in a short time?

OBJECTIVE: The aim of the study was to conduct multi-feature mismatch negativity (MMN) implementations and identify via a test-retest study the reliability of MMN responses obtained through a 5-stimulus version of the MMN paradigm. It was also aimed to identify a reliable MMN recording number by comparing the MMN responses obtained under conditions of ten and four recordings conditions while making the recording time shorter. METHODS: Twenty-one healthy volunteers, aged between 18 and 36 years, were included in the study. A 5-stimulus version of the multi-feature MMN paradigm was presented to participants. Ten recordings were obtained for each participant under both test and retest conditions. The MATLAB program was utilized in the evaluation of MMN amplitude and latency. The Fz was chosen for the statistical analysis. Four of the ten recordings were chosen at random, and statistical analyses were performed again for those four recordings. RESULTS: There was no statistically significant difference in amplitudes obtained from test and retest conditions with ten recordings. With four recordings, for frequency, intensity, duration, and gap deviants, there were no statistically significant differences between amplitudes obtained under test and retest conditions. However, there was a statistically significant difference between amplitudes of the location deviant. No statistically significant difference was observed among latencies under test-retest conditions with both ten and four recordings. CONCLUSIONS: These findings demonstrate that MMN amplitudes could be used reliably as short-time evaluations with four recordings, but more recordings are required for MMN latencies. In terms of practicality, four recordings are more advantageous and comfortable for both clinicians and patients in MMN practice. SIGNIFICANCE: When behavioral tests are required, MMN is regarded as an objective test that can be used reliably for adults, children, and infants who cannot be evaluated using behavioral methods. It is concluded that conditions with four recordings aremore advantageous and comfortable for both clinicians and patients in MMN practice.

Gender Effects on Binaural Speech Auditory Brainstem Response.

BACKGROUND: The speech auditory brainstem response is a tool that provides direct information on how speech sound is temporally and spectrally coded by the auditory brainstem. Speech auditory brainstem response is influenced by many variables, but the effect of gender is unclear, particularly in the binaural recording. Studies on speech auditory brainstem response evoked by binaural stimulation are limited, but gender studies are even more limited and contradictory. This study aimed at examining the effect of gender on speech auditory brainstem response in adults. METHODS: Time- and frequency-domain analyses of speech auditory brainstem response recordings of 30 healthy participants (15 women and 15 men) aged 18-35 years with normal hearing and no musical education were obtained. For each adult, speech auditory brainstem response was recorded with the syllable /da/ presented binaurally. Peaks of time (V, A, C, D, E, F, and O) and frequency (fundamental frequency, first formant frequency, and high frequency) domains of speech auditory brainstem response were compared between men and women. RESULTS: V, A, and F peak latencies of women were significantly shorter than those of men (P< .05). However, no difference was found in the peak amplitude of the time (P > .05) or frequency domain between women and men (P > .05). CONCLUSION: Gender differences in binaural speech auditory brainstem response are significant in adults, particularly in the time domain. When speech stimuli are used for auditory brainstem responses, normative data specific to gender are required. Preliminary normative data from this study could serve as a reference for future studies on binaural speech auditory brainstem response among Turkish adults.

Effects of aging on event-related potentials to single-cycle binaural beats and diotic amplitude modulation of a tone.

Aim of the study is to determine whether the auditory processing of temporal fine structure (TFS) is affected with normal aging, even in the presence of normal audiometric hearing and fine cognitive state; and, if it is, to see whether a comparable effect is also observed in the processing of a diotic change in sound envelope. The event-related potentials (ERPs) to binaural beats (BBs), which are the responses of the binaural mechanisms processing TFS of a sound, and the ERPs to diotic amplitude modulation (AM) stimuli, which are the responses of the monaural mechanisms processing the changes in its envelope, were recorded from thirteen young university students and ten senior but active university professors, all with normal hearing in low frequencies. To obtain directly the specific BB responses without confounding monaural frequency change-evoked responses, we used single-cycle BB stimuli with temporary sub-threshold frequency shifts. BBs of a 250-Hz tone and diotic AM of the same tone with similar perceptual salience were presented with 2-second stimulus onset asynchrony. The N1 components of the ERPs to both stimuli displayed notable age-dependent changes in their scalp topography and significant amplitude reduction and latency prolongation in the elderly. These amplitude and latency changes were at similar rates for the two stimulus types, implying that the auditory TFS and envelope processing mechanisms are proportionally affected by physiological aging. These results may serve as control data in future studies investigating the effect of aging-associated cognitive pathologies on auditory TFS processing.

Passive stretching-induced changes detected during voluntary muscle contractions.

Stretching exercises are known for reduction of musculoskeletal stiffness and elongation of electromechanical delay (EMD). However, computing a change in stiffness by means of time delays, detected between onset of electromyographic (EMG), mechanomyographic (MMG) and force signals, can reveal changes in subcomponents (Δt EMG-MMG and Δt MMG-FORCE) of EMD after stretching. In our study, the effect of stretching was investigated while quadriceps femoris (QF) muscle performed isometric contractions. The EMG, MMG, and Force signals were recorded from rectus femoris (RF) and vastus medialis (VM) during five voluntarily isometric contractions at 15°, 30°, and 45° of knee flexion angle, while the leg was positioned on a custom-made device. Subjects in both intervention and control groups underwent same recording procedure before and after stretching. No difference between the baseline repeated contractions (before stretching) was ensured by ANOVA for repeated measures while a difference between PRE and POST was analyzed and concluded based on the effect size results. The EMD did not change; however, subcomponents (Δt EMG-MMG and Δt MMG-FORCE) showed differences within RF and VM muscles after stretching. The 30° knee flexion angle appears to be a position where isometric contraction intensity needs to be carefully monitored during rehabilitation period.

Event-related potentials to single-cycle binaural beats of a pure tone, a click train, and a noise.

There are only few electrophysiological studies on a phenomenon called "binaural beats" (BBs), which is experienced when two tones with frequencies close to each other are dichotically presented to the ears. And, there is no study in which the electrical responses of the brain to BBs of complex sounds are recorded and analyzed. Owing to a recent method based on single-cycle BB stimulation with sub-threshold temporary monaural frequency shifts, we could record the event-related potentials (ERPs) to BBs of a 250-Hz tone as well as those to the BBs of a 250/s click train and to the BBs of a recurrent 4-ms Gaussian noise. Although fundamental components of the click train and noise stimuli were lower in intensity than the tonal stimuli in our experiments, the N1 responses to the BBs of the former two wide-spectrum sounds were recorded with significantly larger amplitudes and shorter latencies than those to the BBs of a tone, suggesting an across-frequency integration of directional information. During a BB cycle of a complex sound, the interaural time differences (ITDs) of the spectral components are all equal to each other at any time; whereas their interaural phase differences (IPDs) are all different. The ITD rather than the IPD should, therefore, be the cue that is relied upon by the binaural mechanism coding the perceived lateral shifts of the sound caused by BBs. This is in line with across-frequency models of human auditory lateralization based on a common ITD, fulfilling a straightness criterion.

Event-related potentials to single-cycle binaural beats and diotic amplitude modulation of a tone.

When two tones with slightly different frequencies are dichotically presented, binaural beats (BBs) are experienced. BBs resulting from the cycling change in interaural phase difference elicit electroencephalographic responses. Because they repeat at short periods, allowing poor recovery of the cortical responses, these steady-state responses have small amplitudes, and their various wave components intermingle and might mask each other. Using single-cycle BBs separated by relatively long inter-onset intervals would be a solution, but introducing a transient interaural frequency shift requires response subtraction which may not be acceptable for non-additive brain responses. The proposed stimulation method employs transient and monaurally subthreshold frequency shifts in opposite directions in the two ears to produce single-cycle BBs of a 250 Hz tone. These shifts are perceived as distinct BBs when presented dichotically, but remain subthreshold when presented monotically. Therefore, no frequency-shift response is elicited, and the specific BB response is obtained with no need for waveform subtraction. We recorded from 19 normal hearing participants the event-related potentials (ERPs) to single-cycle BBs and also to temporary diotic amplitude modulation (AM) with matched perceptual salience. The ERPs to single-cycle BBs presented at 2 s inter-onset intervals had N1-P2 responses with up to seven times larger amplitudes than the conventional steady-state BB responses in the literature. Significant differences were found between the scalp potential distributions of the N1 responses to BB and AM stimuli, suggesting that the cortical sites, where envelope-based level processing and temporal fine structure-based spatial processing of the stimulus take place, are not totally overlapped.

Pre-attentive Mismatch Response and Involuntary Attention Switching to a Deviance in an Earlier-Than-Usual Auditory Stimulus: An ERP Study.

An acoustic stimulus elicits an electroencephalographic response called auditory event-related potential (ERP). When some members of a stream of standard auditory stimuli are replaced randomly by a deviant stimulus and this stream is presented to a subject who ignores the stimuli, two different ERPs to deviant and standard stimuli are recorded. If the ERP to standard stimuli is subtracted from the ERP to deviant stimuli, the difference potential (DP) waveform typically exhibits a series of negative-positive-negative deflections called mismatch negativity (MMN), P3a, and reorienting negativity (RON), which are associated with pre-attentive change detection, involuntary attention switching, and reorienting of attention, respectively. The aim of the present study was to investigate how these pre-attentive processes are affected if the change occurs earlier than its usual timing implied by isochronous standard stimuli. In the MMN paradigm employed, 15% of the standards were randomly replaced by deviant stimuli which differed either in their pitch, their earlier onset time, or in both. Event-related responses to these three deviants [timely pitch change (RTP), earlier onset (REO), earlier pitch change (REP)] and to standards (RS) were recorded from 10 reading subjects. To maintain identical stimulation histories for the responses subtracted from each other, "deviant-standard" difference potentials (DP) for "timely" and "early" pitch deviances were derived as follows: DPTP = RTP - RS and DPEP = REP - REO. Interestingly, the MMN components of the DPs to timely and early pitch deviances had similar amplitudes, indicating that regularity of stimulus timing does not provide any benefit for the pre-attentive auditory change detection mechanism. However, different scalp current density (SCD) dynamics of the MMN/P3a complexes, elicited by timely and early pitch deviances, suggested that an auditory change in a stimulus occurring earlier-than-usual initiates a faster and more effective call-for-attention and causes stronger attention switching than a timely change. SCD results also indicated that the temporal, frontal, and parietal MMN components are simultaneously present rather than emerging sequentially in time, supporting the MMN models based on parallel deviance processing in the respective cortices. Similarity of the RONs to timely and early pitch deviances indicated that reorienting of attention is of the same strength in two cases.

Effect of Consonant Duration on Formation of Consonant-Vowel Syllable Evoked Auditory Cortical Potentials.

OBJECTIVE: To compare P1-N1-P2-N2 response latencies and amplitudes evoked by voiced and unvoiced consonant-vowel syllables (CVS) /bi/-/pi/ and /di/-/ti/ by analyzing how the cortical responses to consonants and vowels interact during the formation of a syllable-evoked response. MATERIALS AND METHODS: Auditory late latency responses were recorded from 12 healthy individuals between the ages of 20 and 40 years with normal hearing while presenting /bi/-/pi/ and /di/-/ti/ tokens and individual consonant-vowel parts of syllables. Amplitude/latency values of P1-N1-P2-N2 responses were compared between /bi/-/pi/ and /di/-/ti/ pairs. Formation of CVS-evoked responses by consonant and vowel responses was also investigated. RESULTS: N1-P2-N2 latencies evoked by /bi/ were significantly shorter than /pi/. P2-N2 amplitudes evoked by /di/ were significantly higher and N2 latencies were shorter than /ti/. N1-P2-N2 peaks of /bi/, /pi/, and /di/ seemed to be combinations of respective peaks of consonant and vowel-evoked responses. For /ti/, P1 and N1 seem to be stemming only from the consonant part, P2 from consonant P2 and vowel N1, and N2 from consonant N2 and vowel P2-N2. CONCLUSION: For both CVS pairs, longer consonant durations resulted in lower amplitudes and/or longer latencies, and this sheds light on why voiced-unvoiced CVSs evoke cortical responses with different features. Obtaining evoked responses to each consonant-vowel part of the syllables among listeners with perceptual difficulties and hearing devices might help to reveal which acoustic cues are not well represented in the auditory brain.

Comparison of Regularity Detection between Individuals with and without Speech-in-Noise Problems using Electrophysiological Methods.

OBJECTIVE: To analyze the cortical representations of auditory regularities and the relation between these representations and speech-in-noise (SIN) abilities and to compare two groups of participants with different SIN abilities on these cortical measures. MATERIALS AND METHODS: In total, 22 participants aged 20-40 years with normal hearing and without noise exposure, brain stem level-processing issues, neurological/psychiatric issues, or related medication were presented with three different stimuli resembling auditory regularities appearing after random sounds as well as a random series of sounds. Participants received a total of 480 stimuli in passive and active phases each (in which they actively detected regularities). Evoked responses were recorded via 20-channel standard electroencephalography (EEG) cap. RESULTS: The groups were not significantly different in terms of evoked potential parameters. A significant negative correlation was observed between amplitudes of responses evoked by decreasing the frequency regularity in the active phase and SIN scores. Response parameters were significantly different between the stimuli. Active phase latencies were shorter and amplitudes were higher than passive phase ones, except for two stimuli. CONCLUSION: Cortical representations of decreasing frequency regularity are promising for revealing the link between SIN and representations of regularity detection. This paradigm is suggested to applicable to individuals with clinical-level SIN problems [hearing aid (HA) and cochlear implant (CI) users, normal-hearing individuals, children with learning problems, children with dyslexia, and others] to reveal which process of SIN mechanism is defective; this is a complicated process with many sub-mechanisms. These results may be utilized in designing CI and HA algorithms (for more robust representations of auditory regularities) and rehabilitation programs.

Neuropsychological, electrophysiological and neurological impairments in patients with obsessive compulsive disorder, their healthy siblings and healthy controls: Identifying potential endophenotype(s).

The etiology of obsessive-compulsive disorder (OCD) has not been clarified. This study aimed to investigate the cognitive, neurological, electrophysiological functions which are reflected in executive functions, memory, visuospatial integration; neurological examination and auditory event related potentials (AERP) (N100, N200, P200 and P300) in patients with OCD, their siblings, and control subjects and to determine potential endophenotypic markers. Thirty-three patients with OCD, 18 siblings and 21 controls; matched for age, gender and years of education were included. Yale Brown Obsessive Compulsive Symptoms Checklist Scale, Hamilton Depression-Rating Scale, an exhaustive neuropscyhological test battery and Neurological Evaluation Scale were administered. Their AERP recordings were obtained. Executive functions and visuospatial integration were highly impaired in patients and slightly in their siblings compared to controls. P200 amplitude was sorted as siblings>patients>controls. P300 amplitude was sorted as patients

The effects of concurrent cognitive tasks on postural sway in healthy subjects / Efeitos de tarefas cognitivas simultâneas no equilíbrio postural em indivíduos saudáveis

ABSTRACT INTRODUCTION: Keeping balance of the upright stance is a highly practiced daily task for healthy adults and is effectively performed without overt attentional control in most. OBJECTIVE: The purpose of this study was to examine the influence of concurrent cognitive tasks on postural sway in healthy participants. METHODS: This was a prospective study. 20 healthy volunteer subjects were included. The cognitive and balance tasks were performed separately and then, concurrently. Postural control task consisted of 6 conditions (C) of the Sensory Organization Test. The cognitive task consisted of digit rehearsal task of varying presentation and varying levels of difficulty. RESULTS: A statistically significant difference was noted between dual task and no task for C1, C2, C3 and C4 Sensory Organization Test scores ( p < 0.05). There was no statistically significant difference between dual task versus non-task for C5, C6 and combined Sensory Organization Test scores ( p > 0.05). CONCLUSION: During dual task, increase has been determined in postural sway for C1, C2, C3 and C4 for all presentation modes and difficulty levels of the cognitive tasks.

RESUMO INTRODUÇÃO: Manter o equilíbrio na postura vertical é uma tarefa cotidiana constantemente praticada por adultos saudáveis, e é efetivamente realizada pela maioria sem a necessidade de um controle atencional. OBJETIVO: A finalidade deste estudo foi examinar a influência de tarefas cognitivas concomitantes no equilíbrio postural de indivíduos saudáveis. MÉTODO: Trata-se de um estudo prospectivo em que participaram 20 voluntários saudáveis. As tarefas cognitivas e de equilíbrio foram realizadas separadamente; e em seguida, realizadas simultaneamente. A tarefa de controle postural consistiu em seis condições (C) do Teste de Organização Sensorial (TOS). A tarefa cognitiva consistiu na repetição de dígitos com apresentações variadas e vários níveis de dificuldade. RESULTADOS: Houve diferença estatisticamente significante entre os escores do TOS para as condições C1, C2, C3 e C4 para "dupla tarefa" vs. "não tarefa" (p < 0,05). Não houve diferença estatisticamente significante entre os escores do TOS para as condições C5 e C6 e para a combinação dos escores do TOS para "dupla tarefa" vs. "não tarefa" (p > 0,05). CONCLUSÃO: Durante a realização de dupla tarefa, foram determinados aumentos na oscilação postural para as condições C1, C2, C3 e C4 para todos os modos de apresentação e níveis de dificuldade das tarefas cognitivas.

The effects of concurrent cognitive tasks on postural sway in healthy subjects.

INTRODUCTION: Keeping balance of the upright stance is a highly practiced daily task for healthy adults and is effectively performed without overt attentional control in most. OBJECTIVE: The purpose of this study was to examine the influence of concurrent cognitive tasks on postural sway in healthy participants. METHODS: This was a prospective study. 20 healthy volunteer subjects were included. The cognitive and balance tasks were performed separately and then, concurrently. Postural control task consisted of 6 conditions (C) of the Sensory Organization Test. The cognitive task consisted of digit rehearsal task of varying presentation and varying levels of difficulty. RESULTS: A statistically significant difference was noted between dual task and no task for C1, C2, C3 and C4 Sensory Organization Test scores (p<0.05). There was no statistically significant difference between dual task versus non-task for C5, C6 and combined Sensory Organization Test scores (p>0.05). CONCLUSION: During dual task, increase has been determined in postural sway for C1, C2, C3 and C4 for all presentation modes and difficulty levels of the cognitive tasks.

Connectivity measures in the Poffenberger paradigm indicate hemispheric asymmetries.

The Poffenberger paradigm is a well-known measure of interhemispheric transfer delays, calculated on the basis of the crossed vs uncrossed reaction time difference (CUD). However, the proper interpretation of CUD is extensively debated in the literature. In this study we used connectivity measures in an attempt to interpret CUD from the perspective of functional connectivity. Accordingly, we tried to define functional couplings in the Poffenberger paradigm; we used a simple choice version of the paradigm, and included a stimulation only (SO) condition for comparison. As an index of functional coupling we employed partial directed coherence, exploiting bilateral grouping of the electrodes to compute intra-and interhemispheric connection weight ratios (CWRs). Our findings indicated modulations in functional weights in relation to the SO condition, rather than the crossed and uncrossed conditions, such that the response executed by the right hemisphere yielded a decrease in intra-, yet an increase in interhemispheric CWRs, whereas the left hemisphere interactions showed connectivity patterns similar to the SO condition irrespective of the side of movement. Overall, our results suggest modulation of connectivity in the same/similar system, which was found to be optimized, in terms of hemispheric asymmetries, to different tasks.

Electrophysiological assessment of the effects of obstructive sleep apnea on cognition.

We used electrophysiological measures to investigate the effects of obstructive sleep apnea on attention, learning, and memory. Thirty subjects (OSA group, n = 15, control group n = 15) participated in n-back tests, accompanied by P300 recordings, to investigate working memory and attention. The mirror-drawing test was used to study procedural memory, and the trail-making test (TMT) was used to evaluate divided attention and executive function. No significant group difference in reaction time was found in the 0-back and 1-back tests. In the 2-back test, reaction times of patients were longer than those of the control group. No P300 wave was obtained in the OSA group in any (0-, 1-, or 2-back) n-back test. In contrast, in the control group, significant P300 waves were recorded except for the 2-back test. The mirror-drawing scores were unaffected by sleep apnea. There was no difference between groups in the TMT-A test on any of the trials. Although no group difference was found in the first or second trials of the TMT-B test, OSA patients were less successful in learning on the third trial. According to our study results, OSA affects attention and executive function adversely however, we could not detect a significant effect on working or procedural memory.

Significant variations in Weber fraction for changes in inter-onset interval of a click train over the range of intervals between 5 and 300 ms.

It is a common psychophysical experience that a train of clicks faster than ca. 30/s is heard as one steady sound, whereas temporal patterns occurring on a slower time scale are perceptually resolved as individual auditory events. This phenomenon suggests the existence of two different neural mechanisms for processing of auditory sequences with fast and slow repetition rates. To test this hypothesis we used Weber's law, which is known to be valid for perception of time intervals. Discrimination thresholds and Weber fractions (WFs) for 12 base inter-click intervals (ICIs) between 5 and 300 ms were measured from 10 normal hearing subjects by using an "up-down staircase" algorithm. The mean WF, which is supposed to be constant for any perceptual mechanism according to Weber's law, displayed significant variation with click rate. WFs decreased sharply from an average value of around 5% at repetition rates below 20 Hz to about 0.5% at rates above 67 Hz. Parallel to this steep transition, subjects reported that at rates below 20 Hz they perceived periodicity as a fast tapping rhythm, whereas at rates above 50 Hz the perceived quality was a pitch. Such a dramatic change in WF indicated the existence of two separate mechanisms for processing the click rate for long and short ICIs, based on temporal and spectral features, respectively. A range of rates between 20 and 33 Hz, in which the rate discrimination threshold was maximum, appears to be a region where both of the presumed time and pitch mechanisms are relatively insensitive to rate alterations. Based on this finding, we speculate that the interval-based perception mechanism ceases to function at around 20 Hz and the spectrum-based mechanism takes over at around 33 Hz; leaving a transitional gap in between, where neither of the two mechanisms is as sensitive. Another notable finding was a significant drop in WF for ICI = 100 ms, suggesting a connection of time perception to the electroencephalography alpha rhythm.

Event-related potentials to changes of rhythmic unit: differences between musicians and nonmusicians.

We investigated whether the expected differences between musicians and nonmusicians in their ability to detect a rhythm change were reflected in their event-related potentials (ERPs) and, if reflected, how these ERP differences associated with behavioral indices. Stimuli were three consecutive and equally spaced drum beats followed by a rest period to form a rhythmic unit (RU). By using three different inter-beat periods, three RUs were produced. Combinations of these RUs served as the "target/standard" pairs of an oddball sequence. In four different experiments, we tried two RU-change types each with two levels of detection difficulty. ERPs were recorded from the F3, Fz, F4, Cz and Pz scalp sites of 12 musicians and 12 nonmusicians. RT, hit and false-alarm rates were also measured. The data have shown with high statistical confidence that, associated with the musicians' better detection performance and shorter RTs, their ERP P3 to rhythm changes peaked significantly earlier and was significantly larger compared to nonmusicians. Intergroup ERP differences allowed above 90% correct classification. This study has also showed that not only violations of relatively complex musical regularities, but very simple rhythmic unit alterations could lead to significant P3 differences between musicians and nonmusicians. The high accuracy of the musician/nonmusician classification based only on their P3 data strongly supported the hypothesis that sensory and/or cognitive advantage of musicians in detecting rhythm changes does reflect in their P3.

Lamotrigine augmentation in patients with schizophrenia who show partial response to clozapine treatment.

BACKGROUND: Several placebo controlled studies investigating lamotrigine augmentation of clozapine in schizophrenia patients with partial response have shown varying results. The aim of this study was to further investigate the efficacy and safety of this augmentation strategy, and its effect on the glutamatergic system through utilizing mismatch negativity (MMN) component of auditory event related potentials. METHODS: The study was designed to evaluate the efficacy and safety of lamotrigine augmentation of clozapine in a 12-week, double-blind, placebo-controlled, prospective, randomized design. Thirty-four patients diagnosed according to DSM-IV schizophrenia criteria and with partial response to clozapine were included. Patients were randomized to 25mg/day of lamotrigine or placebo, gradually increasing up to 200mg/day on the 6th week. The change in psychopathology was assessed with Positive and Negative Syndrome (PANSS), Calgary Depression (CDS) and Clinical Global Impression-Severity (CGI-S) scales. A neuropsychological test battery was administered and MMN measurements were also obtained at baseline and endpoint. Safety evaluation included physical examination, UKU Side Effect Rating Scale (UKU) assessment and serum drug level measurements. RESULTS: No significant differences were found between the two treatment groups in PANSS Positive and General Psychopathology, CDS, neurocognitive test and UKU scores, as well as MMN measurements. PANSS Total, Negative and CGI-S scores showed significant improvement compared to lamotrigine in the placebo group. CONCLUSION: This study did not show any benefit of augmentation of clozapine with lamotrigine in schizophrenia patients with partial response. The need for further investigation of other augmentation strategies of clozapine in partially responsive schizophrenia patients is evident.

Neuropsychological performance and auditory event related potentials in schizophrenia patients and their siblings: a family study.

BACKGROUND: Various neuropsychological domains, and P300 auditory event-related potentials (ERP) and mismatch negativity (MMN) exhibit abnormalities in schizophrenia patients and their first-degree relatives. The aims of this study were to compare cognitive and P300/MMN measurements in schizophrenia patients, their siblings, and controls, and to identify the degree of familial influence on each measure. METHODS: Thirty patients diagnosed with schizophrenia according to DSM-IV, 20 unaffected siblings and 25 healthy controls were able to complete all neuropsyhological and neurophysiological assessments. All participants were administered SCID-I and the patients were also evaluated regarding symptom severity and functioning. Neuropsychological battery testing results and P300/MMN measurements were obtained for all the participants. RESULTS: Both schizophrenia patients and their siblings had lower working memory, as measured by the Auditory Consonant Trigram Test (ACT), and lower MMN amplitude scores than the controls. In addition, the patients had lower attention, verbal memory, executive function, visuomotor speed, and figural memory scores than both the siblings and controls, and lower verbal fluency scores than controls. MMN and P300 amplitudes were lower and P300 latency longer in the schizophrenia patients, as compared to controls. P300 latency was also longer in the schizophrenia patients as compared to siblings and, MMN amplitudes were significantly lower in the siblings compared to controls. Working memory performance measured by ACT significantly predicted inclusion in both the patient and sibling groups and showed significant familial influence. MMN amplitude significantly predicted inclusion only to the patient group and did not show significant familial influence. CONCLUSION: The schizophrenia patients exhibited impairment in various cognitive domains and P300/MMN measurements, versus impairment only in working memory and MMN amplitude in their siblings. Working memory seems to have a relatively strong familial influence among all the neuropsychological and neurophysiological parameters evaluated.

Ankle clonus and its relationship with the medium-latency reflex response of the soleus by peroneal nerve stimulation.

Ankle clonus and soleus medium-latency reflex are stretch-induced responses. Clonus is traditionally considered to be the result of oscillation in the group Ia mediated spinal stretch reflex but the soleus medium-latency reflex response originates mainly from the activation of group II afferents. The medium latency reflex response (MLR) was recorded in soleus muscle by peroneal nerve stimulation and clonus beats were recorded in soleus muscle using EMG in 19 spastic patients. The dorsiflexion (DF) and plantarflexion (PF) times of clonus and the half-period were calculated based on accelerometric measurements in 11 patients. The MLR of the soleus was 73.63 ± 8.9 ms. The half-period of the clonus was 79.34 ± 12.31 ms. The difference between the MLR and half-period was significant. The PF was 71.75 ± 6.73 ms, and the DF was 88.63 ± 10.83 ms. The difference between the soleus MLR and PF part of the clonus beat was not significant. The PF part of the clonus beat is due to soleus muscle contraction and controlled by the neural part of the oscillation. There may be relationship between the soleus MLR and the PF part of the clonus. Clonus is considered to be the result of oscillations in the group Ia spinal stretch reflex, but there is sufficient time for group II afferents to be involved.

Refractoriness, habituation, and mismatch effects in the auditory event-related potential to alternating stimuli.

Amplitude enhancement in the N1 component of auditory event-related potentials (ERPs) to alternately presented sounds has been referred as a typical example for the effect of release from neural refractoriness. We tested this hypothesis to see whether some other effects also contribute to this phenomenon. Two tones of different frequencies were presented singly or in pairs, and ERPs were recorded using monotonous (mnt) and alternating (alt) sequences of these stimuli. Comparison of the 'alt-mnt' difference waveforms recorded with single and paired stimuli supported the refractoriness hypothesis. A mismatch negativity-like wave, however, was also observed, questioning the constraint of 'at least two consecutive standards before deviant' presumed in most mismatch negativity studies. This paradigm made it possible to delineate the ERP components related to refractoriness and mismatch detection processes.