Humans have been ingesting mindand mood-altering substances for millennia, but it has only rather recently become possible to begin to elucidate drug mechanisms of action and to use this information, along with our burgeoning knowledge of neuroscience, to design drugs intended to have a specific effect. And though most people think of pharmaceuticals as “medicine,” it has become increasingly popular to discuss the possibilities for the use of drugs in enhancement, or improvement of “human form or functioning beyond what is necessary to sustain or restore good health” (E.T. Juengst; in Parens, 1998, p 29).
Some (transhumansits) believe that enhancement may not only be possible, but that it may even be a moral duty. Others (bioconservatives) fear that enhancement may cause us to lose sight of what it means to be human altogether. It is not the intention of this article to advocate enhancement or to denounce it. Instead, let’s review some of the drugs (and/or classes of drugs) that have been identified as the most promisingly cognitive- or mood-enhancing. Many of the drugs we will cover can be read about in further depth in Botox for the brain: enhancement of cognition, mood and pro-social behavior and blunting of unwanted memories (Jongh, R., et al., Neuroscience and Biobehavioral Reviews 32 (2008): 760-776).
Of most importance in considering potentially cognitive enhancer drugs is to keep in mind that, to date, no “magic bullets” appear to exist. That is, there are no drugs exhibiting such specificity as to have only the primary, desired effect. Indeed, a general principle of trade-offs (particularly in the form of side effects) appears to exist when it comes to drug administration for any purpose, whether treatment or enhancement. Such facts may constitute barriers to the practical use of pharmacological enhancers and should be taken into consideration when discussing the ethics of enhancement.
Some currently available cognitive enhancers include donepezil, modafinil, dopamine agonists, guanfacine, and methylphenidate. There are also efforts underway to develop memory-enhancing drugs, and we will discuss a few of the mechanisms by which they are proposed to act. Besides cognitive enhancement, the enhancement of mood and prosocial behavior in normal individuals are other types of enhancement that may be affected pharmacologically, most usually by antidepressants or oxytocin. Let’s briefly cover the evidence for the efficacy of each of these in enhancing cognition and/or mood before embarking on a more general discussion of the general principles of enhancement and ethical concerns.
One of the most widely cited cognitive enhancement drugs is donepezil (Aricept®), an acetylcholinesterase inhibitor. In 2002, Yesavage et al. reported the improved retention of training in healthy pilots tested in a flight simulator. In this study, after training in a flight simulator, half of the 18 subjects took 5 mg of donepezil for 30 days and the other half were given a placebo. The subjects returned to the lab to perform two test flights on day 30. The donepezil group was found to perform similarly to the initial test flight, while placebo group performance declined. These results were interpreted as an improvement in the ability to retain a practiced skill. Instead it seems possible that the better performance of the donepezil group could have been due to improved attention or working memory during the test flights on day 30.
Another experiment by Gron et al. (2005) looked at the effects of donepezil (5 mg/day for 30 days) on performance of healthy male subjects on a variety of neuropsychological tests probing attention, executive function, visual and verbal short-term and working memory, semantic memory, and verbal and visual episodic memory. They reported a selective enhancement of episodic memory performance, and suggested that the improved performance in Yesavage et al.’s study is not due to enhanced visual attention, but to increased episodic memory performance.
Ultimately, there is scarce evidence that donepezil improves retention of training. Better designed experiments need to be conducted before we can come to any firm conclusions regarding its efficacy as a cognitive-enhancing.
The wake-promoting agent modafinil (Provigil®) is another currently available drug that is purported to have cognitive enhancing effects. Provigil® is indicated for the treatment of excessive daytime sleepiness and is often prescribed to those with narcolepsy, obstructive sleep apnea, and shift work sleep disorder. Its mechanisms of action are unclear, but it is supposed that modafinil increases hypothalamic histamine release, thereby promoting wakefulness by indirect activation of the histaminergic system. However, some suggest that modafinil works by inhibiting GABA release in the cerebral cortex.
In normal, healthy subjects, modafinil (100-200 mg) appears to be an effective countermeasure for sleep loss. In several studies, it sustained alertness and performance of sleep-deprived subjects(up to 54.5 hours) and has also been found to improve subjective attention and alertness, spatial planning, stop signal reaction time, digit-span and visual pattern recognition memory. However, at least one study (Randall et al., 2003) reported “increased psychological anxiety and aggressive mood” and failed to find an effect on more complex forms of memory, suggesting that modafinil enhances performance only in very specific, simple tasks.
The dopamine agonists d-amphetamine, bromocriptine, and pergolide have all been shown to improve cognition in healthy volunteers, specifically working memory and executive function. Historically, amphetamines have been used by the military during World War II and the Korean War, and more recently as a treatment for ADHD (Adderall®). But usage statistics suggest that it is commonly used for enhancement by normal, healthy people—particularly college students.
Interestingly, the effect of dopaminergic augmentation appears to have an inverted U-relationship between endogenous dopamine levels and working memory performance. Several studies have provided evidence for this by demonstrating that individuals with a low workingmemory capacity benefit from greater improvements after taking a dopamine receptor agonist, while high-span subjects either do not benefit at all or show a decline in performance.
Guanfacine (Intuniv®) is an α2 adrenoceptor agonist, also indicated for treatment of ADHD symptoms in children, but by increasing norepinephrine levels in the brain. In healthy subjects, guanfacine has been shown to improve visuospatial memory (Jakala et al., 1999a, Jakala et al., 1999b), but the beneficial effects were accompanied by sedative and hypotensive effects (i.e., side effects). Other studies have failed to replicate these cognitive enhancing effects, perhaps due to differences in dosages and/or subject selection.
Methylphenidate (Ritalin®) is a well-known stimulant that works by blocking the reuptake of dopamine and norepinephrine. In healthy subjects, it has been found to enhance spatial workingmemory performance. Interestingly, as with dopamine agonists, an inverted U-relationship was seen, with subjects with lower baseline working memory capacity showing the greatest improvement after methylphenidate administration.
Future targets for enhancing cognition are generally focused on enhancing plasticity by targeting glutamate receptors (responsible for the induction of long-term potentiation) or by increasing CREB (known to strengthen synapses). Drugs targeting AMPA receptors, NMDA receptors, or the expression of CREB have all shown some promise in cognitive enhancement in animal studies, but little to no experiments have been carried out to determine effectiveness in normal, healthy humans.
Beyond cognitive enhancement, there is also the potentialfor enhancement of mood and pro-social behavior. Antidepressants are the first drugs that come to mind when discussing the pharmacological manipulation of mood, including selective serotonin reuptake inhibitors (SSRIs). Used for the treatment of mood disorders such as depression, SSRIs are not indicated for normal people of stable mood. However, some studies have shown that administration of SSRIs to healthy volunteers resulted in a general decrease of negative affect (such as sadness and anxiety) and an increase in social affiliation in a cooperative task. Such decreases in negative affect also appeared to induce a positive bias in information processing, resulting in decreased perception of fear and anger from facial expression cues.
Another potential use for pharmacological agents in otherwise healthy humans would be to blunt unwanted memories by preventing their consolidation.Thismay be accomplished by post-training disruption of noradrenergic transmission (as with β-adrenergic receptor antagonist propranolol). Propranolol has been shown to impair the long-term memory of emotionally arousing stories (but not emotionally neutral stories) by blocking the enhancing effect of arousal on memory (Cahill et al., 1994). In a particularly interesting study making use of patients admitted to the emergency department, post-trauma administration of propranolol reduced physiologic responses during mental imagery of the event 3 months later (Pitman et al., 2002). Further investigations have supported the memory blunting effects of propranolol, possibly by blocking the reconsolidation of traumatic memories.
Reviewing these drugs and their effects leads us to some general principles of cognitive and mood enhancement. The first is that many drugs have an inverted U-shaped dose-response curve, where low doses improve and high doses impair performance.This is potentially problematic for the practical use of cognition enhancers in healthy individuals, especially when doses that are most effective in facilitating one behavior simultaneously exert null or detrimental effects on other behaviors.
Second, a drug’s effect can be “baseline dependent,” where low-performing individuals experience greater benefit from the drug while higher-performing individuals do not see such benefits (which might simply reflect a ceiling effect), or may, in fact, see a deterioration in performance (which points to an inverted U-model). In the case of an inverted U-model, low performing individuals are found on the up slope of the inverted U and thus benefit from the drug, while high-performing individuals are located near the peak of the inverted U already and, in effect, experience an “overdose” of neurotransmitter that leads to a decline in performance.
Trade-offs exist in the realm of cognitive enhancing drugs as well. As mentioned, unwanted “side effects” are often experienced with drug administration, ranging from mild physiological symptoms such as sweating to more concerning issues like increased agitation, anxiety, and/or depression.
More specific trade-offs may come in the form of impairment of one cognitive ability at the expense of improving another. Some examples of this include the enhancement of long-term memory but deterioration of working memory with the use of drugs that activate the cAMP/protein kinase A (PKA) signaling pathway. Another tradeoff could occur between the stability versus the flexibility of long-term memory, as in the case of certain cannabinoid receptor antagonists which appear to lead to more robust long-term memories, but which also disrupt the ability of new information to modify those memories. Similarly, a trade-off may exist between stability and flexibility of working memory. Obviously, pharmacological manipulations that increase cognitive stability at the cost of a decreased capacity to flexibly alter behavior are potentially problematic in that one generally does not wish to have difficulty in responding appropriately to change.
Lastly, there is a trade-off involving the relationship between cognition and mood. Many mood-enhancing drugs, such as alcohol and even antidepressants, impair cognitive functioning to varying degrees. Cognition-enhancing drugs may also impair emotional functions. Because cognition and emotion are intricately regulated through interconnected brain pathways, inducing change in one area may have effects in the other. Much more research remains to be performed to elucidate these interactions before we can come to any firm conclusions.
Again, though it is not the place of this article to advocate or denounce the use of drugs for human enhancement, obviously there are considerable ethical concerns when discussing the administration of drugs to otherwise healthy human beings. First and foremost, safety is of paramount importance. The risks and side-effects, including physical and psychological dependence, as well as long-term effects of drug use should be considered and weighed heavily against any potential benefits.
Societal pressure to take cognitive enhancing drugs is another ethical concern, especially in light of the fact that many may not actually produce benefits to the degree desired or expected. In the same vein, the use of enhancers may give some a competitive advantage, thus leading to concerns regarding fairness and equality (as we already see in the case of physical performance-enhancing drugs such as steroids). Additionally, it may be necessary, but very difficult, to make a distinction between enhancement and therapy in order to define the proper goals of medicine, to determine health-care cost reimbursement, and to “discriminate between morally right and morally problematic or suspicious interventions” (Parens, 1998). Of particular importance will be determining how to deal with drugs that are already used off-label for enhancement. Should they be provided by physicians under certain conditions? Or should they be regulated in the private commercial domain?
There is an interesting argument that using enhancers might change one’s authentic identity—that enhancing mood or behavior will lead to a personality that is not really one’s own (i.e., inauthenticity), or even dehumanization—while others argue that such drugs can help users to “become who the really are,” thereby strengthening their identity and authenticity. Lastly, according to the President’s Council on Bioethics, enhancement may “threaten our sense of human dignity and what is naturally human” (The President’s Council, 2003). According to the Council, “the use of memory blunters is morally problematic because it might cause a loss of empathy if we would habitually ‘erase’ our negative experiences, and because it would violate a duty to remember and to bear witness of crimes and atrocities.” On the other hand, many people believe that we are morally bound to transcend humans’ basic biological limits and to control the human condition. But even they must ask: what is the meaning of trust and relationships if we are able to manipulate them?
These are all questions without easy answers. It may be some time yet before the ethical considerations of human cognitive and mood enhancement really come to a head, given the apparently limited benefits of currently available drugs. But we should not avoid dealing with these issues in the meantime; for there will come a day when significant enhancement, whether via drugs or technological means, will be possible and available. And though various factions may disagree about the morality of enhancement, one thing is for sure: we have a moral obligation to be prepared to handle the consequences of enhancement, both positive and negative.
Originally published as an article (in the Cooler Minds Prevail series) in Cryonics magazine, December, 2013