Neurons come and neurons go – maintaining the brain
Now that we embrace the concept of brain plasticity, it is useful to expand our attention to the broader picture of what happens to neural tissue, whether gain or loss. We know that the brain changes throughout life in relation to experience, behaviour and exposure.
In this light, there is a vast scope for investigation into the neural impact of almost everything that might enter our experience. That potentially opens the door to a wide range of investigation and a plethora of information that might confuse as much as it informs. The resolution may be to simply shift focus from the magnitude of potential information and begin the adventure of discovery and revelation that research enables.
To that end a paper caught my eye that looks at neural degeneration and cannabis. Giovanni Battistella and his colleagues at the University of Lusanne in Switzerland recently published in Neuropharmacology (39:2041-48). The impact of regular use could be seen in a reduction in grey matter in the medial temporal cortex, parrahippocampal gyrus, right temporal pole, left insula, precuneus and orbitofrontal cortex (OFC). Interestingly there was an increase in grey matter volume in the cerebellum.
The areas affected are those with high numbers of cannabinoid receptors, CB1. The experiential effects include deficits in decision making, which is strongly related to deficits in the ventromedial prefrontal cortex (VMPFC) which is proximal to the OFC. Choices that bring immediate benefits often override long term consequences, even if those consequences are negative. Deficits in the insula, OFC and precuneus negatively impact motivation and also affective elements related to the sense of self. The cannabis ‘high’ is experienced as slowness and dullness of mental activity, a sense of euphoria that is related to heightened incongruence of immediate circumstance – everything just seems so funny – disruption to regulation of cravings – the munchies – and sometimes a fearful response regarding personal awareness – paranoia. The loss of grey matter seen in this paper indicates that some of these temporary issues may become permanent for the heavy and persistent smoker as the brain changes in response to excessive doses of chemicals in cannabis.
These disturbing results give some pause in relation to the increasing use of cannabis for medical purposes. Cannabis oil has become an almost miracle cure for some people with intractable epilepsy. Anecdotally, it is saving lives. Colorado in the USA is leading the way in the medical utilization of cannabis. Australia still has a blanket ban on the cannabis species, despite the fact that many species have very little of the psychotrophic chemical THC. These are usually termed ‘hemp’ plants. There is clearly much work to be done in unravelling the neurobiological impacts of chemical in the cannabis species. There are benefits and cautions that need to be differentiated so that the most benefit can be derived from this somewhat maligned species of plant.
I hope to bring our attention to other papers that show beneficial plasticity in the future. This is a fascinating time in neuroscience and we need to continually try and maintain some insight into the impact on the human experience at the same time that we are advancing our technical knowledge.
Battistella, G., Forari, E., Annoni, J-M., Chtioui, H., Dao, K., Fabritius, M., Favrat, B., Mall, J-F., Maeder, P. & Giroud, C. (2014) Long-term effects of cannabis on brain structure. Neurpsychopharmacology 39: 2041-2048.