Is borderline personality a particularly right hemispheric disorder? A study of P3a using single trial analysis.

OBJECTIVE: To test the hypothesis that borderline personality disorder is a manifestation of a particularly right hemispheric disturbance, involving deficient higher order inhibition, and to consider the therapeutic implications of the findings.

METHODS: A cohort of 17 medication free borderline patients were compared with 17 age and sex matched controls by means of a study of p3a, which reflects the activity of one of the two main generators of the P300 (P3) of the event-related-potential. P3b reflects the output of the other generator. P3a, an aspect of the attentional system, depends upon prefrontally connected neurocircuitry. P3b is underpinned by a particularly parietally connected neural system. Using an oddball paradigm, P3a was extracted from the responses to targets using a novel single trial analysis.

RESULTS: In borderline patients, over homologous electrode sites, p3a amplitudes, but not latencies, were significantly larger in the right hemisphere compared with the left. The differences were most marked fronto-centrally. No such difference was shown in the control subjects. P3a at right hemisphere sites was significantly larger in borderline compared with control patients. There was no significant difference between the groups for the left hemisphere sites.

CONCLUSIONS: The abnormally large amplitudes of P3a at right hemisphere sites in borderline patients together with the failure of habituation of P3a, are consistent with deficient inhibitory activity. Discussion of the findings suggest that they may reflect impeded maturation of the fronto-medial processing systems which, it is argued, may be a consequence of the typical early environment of those with the borderline condition. This suggestion leads to a consideration of optimal therapeutic behaviour in this condition, in particular for 'matching' or 'analogical' responsiveness.