Rodney J. Croft

Response inhibition deficits in obsessive–compulsive disorder

Difficulty inhibiting irrelevant information may play a central role in the aetiology of obsessive-compulsive disorder (OCD). The aim of the present study was to determine whether OCD subjects (n=20) exhibit deficits in behavioural and cognitive inhibition compared with a clinical control group diagnosed with panic disorder (n=20). All subjects were administered a Go/Nogo task (a measure of behavioural inhibition) and a Stroop test (a measure of cognitive inhibition). OCD subjects made more commission errors on the Go/Nogo task, and they made more errors and displayed longer reaction times on the interference trial of the Stroop task. Trends towards correlations were observed between OCD severity scores and Stroop reaction time, where the more severe the OCD symptoms the faster was the response. No correlations between clinical symptomatology or subject demographics and the Go/Nogo task were observed. It was demonstrated that OCD subjects exhibit deficits in behavioural and cognitive inhibition, which together may underlie the repetitive symptomatic behaviours of the disorder, such as compulsions and obsessions.

Acute mobile phone operation affects neural function in humans

OBJECTIVES Mobile phones (MP) are used extensively and yet little is known about the effects they may have on human physiology. There have been conflicting reports regarding the relation between MP use and the electroencephalogram (EEG). The present study suggests that this conflict may be due to methodological differences such as exposure durations, and tests whether exposure to an active MP affects EEG as a function of time. METHODS Twenty-four subjects participated in a single-blind fully counterbalanced cross-over design, where both resting EEG and phase-locked neural responses to auditory stimuli were measured while a MP was either operating or turned off. RESULTS MP exposure altered resting EEG, decreasing 1-4 Hz activity (right hemisphere sites), and increasing 8-12 Hz activity as a function of exposure duration (midline posterior sites). MP exposure also altered early phase-locked neural responses, attenuating the normal response decrement over time in the 4-8 Hz band, decreasing the response in the 1230 Hz band globally and as a function of time, and increasing midline frontal and lateral posterior responses in the 30-45 Hz band. CONCLUSIONS Active MPs affect neural function in humans and do so as a function of exposure duration. The temporal nature of this effect may contribute to the lack of consistent results reported in the literature.

Is the P300 wave an endophenotype for schizophrenia? A meta-analysis and a family study

INTRODUCTION We assessed the usefulness of the P300 wave as endophenotype for schizophrenia by means of a meta-analysis of the literature as well as our own family study. METHOD Meta-analysis: We conducted a systematic search for articles published between 1983 and 2003 that reported P300 measures in non-psychotic relatives of schizophrenic patients and in healthy controls. Meta-regression analyses were performed using a random effects procedure. The pooled standardized effect size (PSES) was calculated as the difference between the means of the two groups divided by the common standard deviation. Local study: We examined the P300 wave with a standard two-tone oddball paradigm in 30 patients with schizophrenia, 40 non-psychotic relatives, and 40 controls using linear mixed models. RESULTS Meta-analysis: We pooled 472 relatives and 513 controls. The P300 amplitude was significantly reduced in relatives (PSES = 0.61; 95% CI: 0.30 to 0.91; P < 0.001). The P300 latency was significantly delayed in relatives (PSES of -0.50; 95% CI: -0.88 to -0.13; P = 0.009]. Local study: The patients showed a trend for amplitude reductions (P = 0.06) and significant latency delays (P < 0.01). The relatives displayed normal amplitude but had significant latency delays (P = 0.01). The P300 amplitude and especially the P300 latency are promising alternative phenotypes for genetic research into schizophrenia.

Chronic MDMA (ecstasy) use, cognition and mood.

RationaleIt has been suggested that 3,4-methylenedioxymethamphetamine (MDMA or ecstasy) causes damage to the serotonergic system, and that this damage results in cognitive and mood impairments.ObjectivesTo examine the effect of chronic MDMA usage on a wide battery of cognitive tests and psychological abilities and processes.MethodsIn the present study, the performance of 17 participants with a history of MDMA use was compared to the performance of 15 control subjects on a battery of neuropsychological tests. This battery included tests for depression, immediate word recall, delayed recall, attention and working memory.ResultsResults indicated that the MDMA group had significantly higher scores for depression than the control group, and displayed poorer delayed recall and verbal learning than controls after accounting statistically for the effects of cannabis and depression.ConclusionsThese results suggest that MDMA users exhibit difficulties in coding information into long-term memory, display impaired verbal learning, are more easily distracted, and are less efficient at focusing attention on complex tasks.

Examining the effects of electromagnetic fields emitted by GSM mobile phones on human event-related potentials and performance during an auditory task

OBJECTIVE Due to the widespread use of mobile phones (MP), it is important to determine whether they affect human physiology. The aim of this study was to explore the sensitivity of auditory event-related potentials to electromagnetic emissions. METHODS Twelve participants attended two sessions, 1 week apart. Participants performed an auditory oddball task while they were exposed to an active MP during one session and sham exposure during the other. Each condition lasted 1 h and order was counterbalanced. N100 and P200 latencies and amplitudes were analysed for non-target waveforms, and N200 and P300 latencies and amplitudes were analysed for target waveforms. RESULTS In real relative to sham exposure N100 amplitude and latency to non-targets were reduced, with the reduction larger over midline and right hemisphere sites. P300 latency to targets was delayed in the real exposure condition, however as this difference was greatest at left frontal and left central sites the interpretation of this result is unclear. Reaction time increased in the real relative to sham condition. No difference in accuracy was found. CONCLUSIONS The results suggest that MP exposure may affect neural activity, particularly in proximity to the phone, however caution should be applied due to the small sample size.

Mismatch negativity in schizophrenia: a family study

BACKGROUND Mismatch negativity (MMN) is a measure of cortical activity that occurs in response to a change in auditory stimuli. We investigated whether MMN is a potential marker of genetic vulnerability to schizophrenia by comparing MMN in a group of patients with schizophrenia, their unaffected relatives, and controls. METHOD There are 25 schizophrenic patients, 37 of their unaffected first-degree relatives, and 20 unrelated controls that performed the MMN task. Linear regression with robust standard errors, and accounting for correlations within families, was employed to test for differences in MMN amplitude between the groups. RESULTS Patients had significantly smaller MMN amplitudes compared to both their unaffected relatives and controls at FZ (P<0.01) and at F3 (P=0.01), whereas relatives and controls did not differ at FZ or at F3. No differences were found between any of the groups at F4. Furthermore, we found no strong evidence that the MMN amplitude is a familial trait. CONCLUSIONS Our results confirm that the MMN amplitude is reduced in schizophrenia. However, the MMN does not show a significant familial influence and is normal among the unaffected relatives. We conclude that while the MMN is abnormal in patients with schizophrenia, it is a weak or unreliable marker of vulnerability when applied to subclinical populations, and therefore is unlikely to be an endophenotype for the disorder.

Muscarinic and nicotinic receptor modulation of object and spatial n-back working memory in humans

Working memory impairments in the n-back task in schizophrenia have been linked to sustained deficiency in mesocortical dopamine function. More recently, abnormalities in the cholinergic system have also been documented in schizophrenia, with cortical reductions in both nicotinic and muscarinic receptors. While the cholinergic hypothesis of memory is well established, the role of cholinergic receptors in modulating n-back working memory is not known. We investigated the effects of selective and simultaneous muscarinic and nicotinic antagonism on spatial and object n-back working memory performance. The study was a double-blind, placebo-controlled repeated-measures design in which 12 healthy subjects were tested under four acute treatment conditions; placebo (P), mecamylamine (M), scopolamine (S) and mecamylamine+scopolamine (MS). Muscarinic antagonism with scopolamine significantly impaired both object and spatial n-back working memory, whereas nicotinic antagonism with mecamylamine had little effect. Simultaneous antagonism of both muscarinic and nicotinic receptors produced greater impairments in both object and spatial n-back working memory performance than muscarinic or nicotinic antagonism alone. These results suggest that: (1) both muscarinic and nicotinic receptors may functionally interact to synergistically modulate n-back working memory, and (2) that n-back working memory impairments in schizophrenia may in part be due to reductions in both muscarinic and nicotinic receptors.

Executive functions in obsessive–compulsive disorder: state or trait deficits?

OBJECTIVE Despite the neuropsychology literature providing reliable evidence of impaired executive functions in obsessive-compulsive disorder (OCD), to date it has not been determined whether these deficits are trait-related (independent of symptomatology) or state-dependent (dependent on symptomatology). The current research examines the executive functions in OCD in a comprehensive manner and, for the first time, assesses the stability of these deficits over the developmental course of the disorder. METHOD Using a cross-sectional design, Study 1 examined the executive functions (set shifting, inhibition, planning, verbal fluency and working memory) in 60 subjects (20 actively Symptomatic OCD, 20 Remitted OCD and 20 Panic Disorder). Using a longitudinal design, Study 2 reassessed a subsample of OCD subjects (participants in Study 1) once they reached remitted status. RESULTS Study 1 found that the OCD groups exhibited deficits in set shifting and inhibition relative to Panic Disorder controls; however, no deficits were observed in planning, verbal fluency or working memory. There were no differences found between the Symptomatic and Remitted OCD groups on any of the executive function measures. Study 2 found that the identified executive function deficits in individuals were stable over time and remained unchanged despite symptom remittance. CONCLUSION Current results confirm the presence of specific executive function deficits in OCD, and indicate that these deficits are trait-like in nature.

Effects of radiofrequency electromagnetic fields on the human nervous system

The effects of exposure to radiofrequency electromagnetic fields (EMF), specifically related to the use of mobile telephones, on the nervous system in humans have been the subject of a large number of experimental studies in recent years. There is some evidence of an effect of exposure to a Global System for Mobile Telecommunication (GSM)-type signal on the spontaneous electroencephalogram (EEG). This is not corroborated, however, by the results from studies on evoked potentials. Although there is some evidence emerging that there may be an effect of exposure to a GSM-type signal on sleep EEG, results are still variable. In summary, exposure to a GSM-type signal may result in minor effects on brain activity, but such changes have never been found to relate to any adverse health effects. No consistent significant effects on cognitive performance in adults have been observed. If anything, any effect is small and exposure seems to improve performance. Effects in children did not differ from those in healthy adults. Studies on auditory and vestibular function are more unequivocal: neither hearing nor the sense of balance is influenced by short-term exposure to mobile phone signals. Subjective symptoms over a wide range, including headaches and migraine, fatigue, and skin itches, have been attributed to various radiofrequency sources both at home and at work. However, in provocation studies a causal relation between EMF exposure and symptoms has never been demonstrated. There are clear indications, however, that psychological factors such as the conscious expectation of effect may play an important role in this condition.

Target‐to‐target interval versus probability effects on P300 in one‐ and two‐tone tasks

The P3(00) is an electrophysiological index of neural processing that varies with such stimulus parameters as interstimulus interval (ISI) and target probability, with a common view being that it reflects an endogenous form of memory update. Building on previous research, we argue that relations between P3 amplitude and both ISI and probability may be attributable to the target-to-target interval (TTI). Employing between-subject (Experiment 1; N = 24) and within-subject (Experiment 2; N = 10) designs, the present paper addresses this by testing subjects on a standard two-tone auditory oddball task as well as a one-tone task. In both studies, P3 amplitude increased and latency decreased linearly with TTI, and these relations were relatively unaffected by ISI or probability. This suggests that ISI and probability per se do not independently affect P3 amplitude, and that TTI offers a strong explanation of the reported relations between P3 amplitude and both ISI and probability.