Auditory P300 study in remittent bipolar child and adolescent population

Abstract

Objectives

Previous studies have revealed P300 abnormality in adult bipolar population, both in acute and euthymic phases and also in their first-degree relatives. To the best of our knowledge there are limited data in the child and adolescent bipolar population. In this study we attempt to record P300 amplitudes and latencies of remittent child and adolescent bipolar patients and compare them with normal controls.

Method

25 remittent child and adolescent bipolar patients and 25 age, sex matched controls were recruited. P300 was recorded using the auditory oddball paradigm.

Results

There was significant increase in latency of P300 at midline, parietal leads, and the frontal and central leads decreased significantly at the parietal and frontal leads in the patient population. Amplitude was more in the patient group as compared to controls.

Conclusion

The present findings of prolonged latency and reduced amplitude of P300 in the remission and the phase of bipolar illness indicate that cognitive processing deficits persist beyond illness and P300 could be a promising candidate endophenotype for future research.

Introduction

Bipolar disorder is characterized by deficits in sustained attention, focusing execution, cognitive flexibility and general cognitive functions. While neurobiological dysregulation is thought to produce these behavioral changes, the mechanisms responsible for bipolar disorder remain obscure. Biological markers sensitive to state changes during the illness (e.g., manic to euthymic) might provide a bridge between behavioral and neurobiological abnormalities. Abnormalities which persist even in euthymic phase may provide insight into trait mechanism (Lenox et al., 2002).

Event-related potential (ERP) as a measure of time-locked EEG activity captures neural activity related to both sensory and cognitive processes. ERPs can be either early and sensory in nature, affected by the physical characteristics of the stimuli, or later and cognitive in nature, affected by the subjective cognitive operations of the subject (Donchin, 1979, Hillyard et al., 1973, Sutton et al., 1965).

The P3 auditory event-related potential is a positive deflection that peaks approximately 300 ms after the onset of an attended target stimulus, such as an infrequently occurring pure tone (oddball) randomly interspersed among frequently occurring, differently pitched pure tones (standards). P3 represents brain activity related to late stage cognitive processes and is relatively independent of stimulus modality, whereas earlier components such as PI, Nl and P2 are influenced primarily by stimulus modality characteristics.

Reduced P3 amplitude has been found in a variety of psychiatric disorders, including schizophrenia (McCarley et al., 1993, Trestman et al., 1996), conduct disorder (Bauer and Hesselbrock, 1999), and alcoholism (Porjesz and Begleiter, 1998). Among healthy subjects, P3 latency has been associated most frequently with measures of working memory (Emmerson et al., 1990, O’Donnell et al., 1992, Polich et al., 1983).

P300 is comparatively less studied in bipolar disorder. Majority studies document an increase in P300 latency (Muir et al., 1991, O’Donnell et al., 2004, Souza et al., 1995) but P300 amplitude reduction in affective disorder is somewhat equivocal. Some studies have shown reduction in amplitude (O’Donnell et al., 2004, Salisbury et al., 1999), but others failed to find so (Souza et al., 1995, Schulze et al., 2008). While most studies have documented P300 abnormality in acutely symptomatic adult patients, stable remitted bipolar patients have been scarcely studied. To our knowledge there are very less data on the child and adolescent bipolar population. In this study we attempt to perform P300 on remittent child and adolescent bipolar patients to assess presence of cognitive deficits in remittent phase of the illness.