My latest news story for Nature describes a new study which explains how marijuana causes impairments in working memory, or the ability to retain information for short periods of time. This is a well known side effect of marijuana, which is unwanted with respect to medicinal use of the drug, but until now the underlying neurobiology was unknown.

The research shows that tetrahydrocanabinol (THC, the psychoactive ingredient in marijuana) impairs working memory by inducing a form of synaptic plasticity that weakens neuronal connections. This could lead to new THC-related drugs that have therapeutic value but do not cause this unwanted effect. More interestingly, though, the findings provide compelling evidence that hitherto neglected brain cells called astrocytes are critical for brain function and play a direct role in cognitive processes.

There are two different types of synapitc plasticity. One of these, called long-term potentiation, strengthens the connections between neurons so that neurotransmission – the process by which signals pass from one nerve cell to another – is more effective. Long-term potentiation is widely believed to underly learning and memory…