Abstract
Previous studies have mostly shown positive effects of cannabis use on cognition in patients with schizophrenia, which could reflect lower neurocognitive vulnerability. There are however no studies comparing whether such cognitive differences have neuronal correlates. Thus, the aim of the present study was to compare whether patients with previous cannabis use differ in brain activation from patients who has never used cannabis. The patients groups were compared on the ability to up-regulate an effort mode network during a cognitive task and down-regulate activation in the same network during a task-absent condition. Task-present and task-absent brain activation was measured by functional magnetic resonance neuroimaging (fMRI). Twenty-six patients with a DSM-IV and ICD-10 diagnosis of schizophrenia were grouped into a previous cannabis user group and a no-cannabis group. An auditory dichotic listening task with instructions of attention focus on either the right or left ear stimulus was used to tap verbal processing, attention, and cognitive control, calculated as an aggregate score. When comparing the two groups, there were remaining activations in the task-present condition for the cannabis group, not seen in the no-cannabis group, while there was remaining activation in the task-absent condition for the no-cannabis group, not seen in the cannabis group. Thus, the patients with previous cannabis use showed increased activation in an effort mode network and decreased activation in the default mode network as compared to the no-cannabis group. It is concluded that the present study show some differences in brain activation to a cognitively challenging task between previous cannabis and no-cannabis schizophrenia patients.
Highlights
It has been shown that cannabis use is more widespread in patients with schizophrenia than in the healthy population (Regier et al, 1990; Arseneault et al, 2004; Barnes et al, 2006)
The aim of the present study was to examine brain activation in patients with schizophrenia with and without a history of previous cannabis use, and to explore if previous neurocognitive differences between these groups have neuronal substrates that could be detectable in an functional magnetic resonance neuroimaging (fMRI) study
CLINICAL, DEMOGRAPHIC DATA There were no significant differences between the two groups for the clinical, dichotic listening (DL), cognitive, and demographic data, the social or general functioning data shown in Table 1, expect for Education [F (1, 22) = 5.93 p = 0.02] and Age of onset [F (1, 22) = 4.62 p > 0.04]
Summary
It has been shown that cannabis use is more widespread in patients with schizophrenia than in the healthy population (Regier et al, 1990; Arseneault et al, 2004; Barnes et al, 2006). A systematic literature review revealed better cognitive functioning in cannabisusing compared to non-cannabis-using patients in a majority of the reviewed 23 studies (Løberg and Hugdahl, 2009). This pattern has been replicated by later studies (DeRosse et al, 2010; Rodriguez-Sanchez et al, 2010), including two meta-analyses (Rabin et al, 2011; Yucel et al, 2012). It is of importance, to differentiate between the consequences of ongoing cannabis use and short-term intoxication effects versus the effects of previous cannabis use as pathway to psychosis (Løberg and Hugdahl, 2009). The authors suggested that the life-time cannabis-using group formed a subgroup with a different cognitive profile
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