Stimulatte'd - The Everyday Neuroscience of Coffee
Updated: Mar 19, 2019
Coffee has unquestionably achieved total world dominance. Since the practice of repurposing the coffee bean into a consumable beverage began some 600 years ago, coffee has gone on to transcend innumerable national barriers and infiltrate the lives of millions. By permeating multiple layers of society, this elixir of life has emerged as a key cultural pillar for many, or for some the only means by which to summon the powers of motivation or conversation.
Some of us may rely on coffee more than we care to admit. It’s conceivable many of us are perhaps unaware of a very real dependency, given how easily we’re able to caffeinate ourselves should we wish to, with a café of choice never more than 5 metres away. It is however caffeine and its psychoactive properties that we really have to thank for our continued and relentless demand for coffee.
For something with such a high consumption rate in our population, there appears to be a striking absence of public knowledge regarding the risks associated with the long-term consumption of caffeine, its short-term cognitive effects, and its mechanism of action more generally. Luckily AxonMagazine has got your back, and we’ve laid out everything you need to know in the form of this delightfully short editorial.
A prominent member of the methylxanthine class, caffeine acts as an antagonist of adenosine, a not-quite-a-neurotransmitter which has the generalised function of inhibiting neuronal activity. Generated extracellularly by virtue of the breakdown of energy-containing molecules, adenosine accumulates over the course of the day, exerting a growing inhibitory effect on the brain until we go to sleep. Glutamate, dopamine and acetylcholine are all neurotransmitters whose release is mediated via pre-synaptic adenosine receptors; as a consequence of reducing their inhibition, caffeine promotes the cognitive effects which are elicited by these neurotransmitters .
Among the most prominent of these effects is the heightened sense of arousal and alertness that we’ve all likely experienced after a particularly intense flat white. Even without the other positive and rewarding effects of caffeine, its ability to keep us alert and focussed is often the only reason why we consume coffee in such large quantities. These heightened states of arousal are a consequence of an increased firing rate in mesopontine cholinergic neurons, an area of the brain found in the brain stem which participates in ascending arousal systems, and is typically inhibited by adenosine. The benefits of being more alert are largely intuitive, although demonstrated experimentally in a number of behavioural studies – for instance, in one study aiming to evaluate the effect of caffeine on sleep deprivation and driving, the administration of caffeine returned subject group’s driving performance back to pre-sleep deprivation levels, in comparison to a placebo condition .
However, we must exercise a touch of caution here – caffeine may indeed make us more alert and place us in a better position to navigate our natural environment, but what of the effects of long-term consumption? For all of us who depend on coffee to help us learn huge, impossibly large volumes of material in short spaces of time, we could actually be shooting ourselves in the foot. Long term consumption of low doses of caffeine has been previously linked to a slowing of hippocampal-dependent learning, reductions to hippocampal neurogenesis, and impaired long-term memory. So, if you’re intent on not just passing your exams, but remembering the material afterwards, it could be sensible to pump the brakes on that 3rd espresso of the morning .
While the hippocampus is experiencing some trouble in this instance, a structure within the striatum called the nucleus accumbens is busy having a good time while it enjoys caffeine-induced increases in extracellular concentrations of dopamine. Interestingly, a dopaminergic fluctuation in this region is proposed to be a principal contributory mechanism toward the rewarding feelings experienced under the influence of psychostimulants such as amphetamines or cocaine. By elbowing adenosine out of the way of its target receptors and relieving the pre and post-synaptic shackles imposed by adenosine upon dopaminergic transmission, caffeine bestows upon us the feel-good sensations .
Sadly, it doesn’t end there, as there also exists a considerable portion of coffee drinkers who occasionally report anxiogenic responses to caffeine. To shed some light on why this could be the case, one study examined possible relationships between different genetic forms (polymorphisms) of two distinct adenosine receptors, and the variation in the reported anxiogenic responses following the administration of caffeine. The results pointed to 2 linked polymorphisms on the A2-adenosine receptor as the genetic culprits underlying caffeine-induced anxiety, namely polymorphisms labelled as ‘1976C>T’ and ‘2592C>Tins’ variants. In contrast to those without these genotypes, greater anxiogenic responses were elicited by caffeine in the 1976C>T and 2592C>Tins genotypic groups. Relatedly, previous research has linked genetic polymorphisms of this variety to panic disorder - this tells us something interesting about the genetic underpinnings of anxiety-based disorders, insofar as they may share common ground with regards to their A2 receptor profile .
So, there you have it – the why’s and how’s of the neuroscience of coffee. In light of this article, an interesting question we could ask of ourselves could be: why is it that sometimes, even for someone with an unfavourable genetic pre-disposition to anxiety, coffee can be a cup of can-do attitude, and other times a red-hot mug of anxiety? What are the many psychopharmacological or neurological factors which determine whether or not you’re going to have a pleasant experience from your latte? If you, the reader, have any thoughts on this topic, then do not hesitate to tweet us at @AxonMagazine.
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