Alterations to pre-pulse inhibition (PPI) in chronic cannabis users are secondary to sustained attention deficits

RationaleGiven the hypothesised association between cannabis use and schizophrenia, and the well documented alterations in pre-pulse inhibition (PPI) that are observed in schizophrenia, it is of interest to examine the effects of cannabis use on PPI.ObjectiveThe objective of the study was to use novel methodology for the measurement and characterisation of attentional modulation of PPI, in order to examine the nature of PPI in chronic cannabis users.MethodsPPI was measured in 34 chronic cannabis users (who were otherwise healthy) and 32 healthy controls, across a range of startling stimulus intensities, during two attention set conditions, one in which they were instructed to attend to the auditory stimuli and one in which they were instructed to ignore the auditory stimuli and focus on a visual task. Curves of best fit were fitted to the startle magnitudes, across the stimulus intensities. A number of reflex parameters were extracted from these logistic functions, each of which reflects a different characteristic of the startle response.ResultsCannabis users failed to show attentional modulation of any of the reflex parameters and showed altered PPI, relative to controls, but only when they were instructed to sustain attention to the auditory stimuli.ConclusionCannabis users showed an attention-dependant alteration in PPI, which appeared to reflect a deficit in sustain attention, and which was different to that which has been observed in schizophrenia using the same methodology.