Schizophrenia is associated with cannabis use and deficits in selective attention.

This study investigated these relationships using habituation of the startle reflex in schizophrenia patients relative to cannabis users during selective attentional tasks.

Participants included 12 healthy controls (CON), 16 healthy cannabis users in the last 12 months (THC), and eight schizophrenia patients (SCZ). Auditory startle reflex was recorded from orbicularis oculi muscle while participants were attending to (Attend Task) or ignoring (Ignore Task) 100 dB startling pulses. Startle habituation was measured as the absolute reduction in startle magnitude on block 2 (last nine trials) vs. block 1 (first nine trials) on each attentional task and in each group.

All three groups were matched on demographics, alcohol, and caffeine consumption. ANCOVA with two within-subject factors (attention and habituation with 2 levels each), one between-subject factor (group with 3 levels), and one covariate (nicotine use which was higher in SCZ vs. CON or THC) showed a significant startle habituation with moderate to large effect sizes in all three groups on the Ignore Task (Cohen's d=0.67 in CON, d=0.59 in THC, d=0.90 in SCZ) but not on the Attend Task. Attentional modulation of the startle reflex occurred only in CON (d=1.33) and THC (d=1.17), but not in SCZ.

Auditory startle habituation depends on selective attention but is not affected by schizophrenia or cannabis use. Deficient attentional modulation of the startle reflex suggests that a more severe deficit in selective attention occurs in schizophrenia relative to cannabis use.