Auditory P300 study in remittent bipolar child and adolescent population
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.
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Subjects
Patients were recruited from Child and Adolescent Psychiatry Unit Outpatient Department of Central Institute of Psychiatry, India. Controls were recruited by newspaper advertisements; control and patient groups were matched for age, gender and social class.
After obtaining informed consent from patients and accompanying guardians, structured diagnostic interviews were performed for all participants using the Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version (Joan
Subject
Subject characteristics are presented in Table 1. The mean age of patients (15.46 years) and controls (15.44 years) was similar and so was the gender distribution among the 2 groups. There was no significant difference between patient and control groups in terms of socioeconomic status (P = 0.097) with most of them belonging to middle socioeconomic status. Clinical characteristics of the patient population are presented in Table 2. The mean age of onset of illness was 13.44 years with duration of
Discussion
To our knowledge, this is the first study of auditory P300 in a remitted child and adolescent bipolar population. We demonstrated significant P300 latency delays at parietal, central, frontal and midline leads in patients compared to controls, with decreased P300 amplitude in parietal and frontal electrodes.
Ethical committee approval
The protocol for above study was reviewed and approved by the Institutional Review Board and the methods used followed the broad definition of the Declaration of Helsinki.
Role of funding source
Nil.
Conflict of interest
None.
Acknowledgements
We thank Dr. Pushpal DeSarkar for helping in writing the protocol and in analysis of data, Dr. Nishant Goyal for helping in data analysis and Dr. Saddichha Sahoo for checking the initial manuscript and data analysis.
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