Magnocellular processing in chronic cannabis users – CAUSA MAP

Cannabis is widely used in industrialised countries. Its consumption has particularly increased during early adolescence, a period when the developing brain is susceptible to environmental exposures. This is crucial since an association between early cannabis consumption and the risk of emerging schizophrenia has been established.
A dysfunction of the glutamatergic system has recently been proposed as a pathophysiological model to explain this association. Indeed, the regulatory role of the endogenous cannabinoid system in glutamate neurotransmitter release is disrupted by chronic administration of THC. By preventing endocannabinoid-mediated control over the homeostasis of glutamate, it has been proposed that exogenous cannabinoids may dramatically affect the process of maturational refinement of cortical neuronal networks, impacting on processes based on neural plasticity such as perceptual learning. This effect could interact with a biological vulnerability on neural maturation, thus leading to schizophrenia. This model has been based on animal experiments and now needs to be confirmed in humans. In this project we target functions that are known to be sensitive to glutamatergic transmission, and we determine the impact of chronic cannabis consumption on these functions.
Measuring early perceptual processing has been used to assess glutamate transmission in schizophrenia: regarding vision, a magnocellular dysfunction in schizophrenia has been well established with a large range of methodologies. Measuring low level cognitive functions has the advantage of being less sensitive to attention, thus eliminating the bias of a non specific generalized attentional deficit.
We propose herein to study the impact of heavy cannabis consumption on magnocellular processing in order to evaluate the functioning of the glutamatergic system. We will also study the consequences of a potential early visual deficit on integrated visual functions refined by perceptual learning.
Magnocellular processing will be appraised in several studies with a contrast sensitivity function, masking and a simultaneity threshold task. ERP will be assessed during these measurements in order to verify that behavioural results are due to early visual impairments. The impact of a magnocellular dysfunction on higher order visual processing will be evaluated in a face recognition task with spatial filtered stimuli. At last we will evaluate whether polymorphisms implied in endocannabinoid system and neuroplasticity differentially modulates magnocellular processing in chronic cannabis users