A recent neuroscience study from Harvard Medical School claims to have discovered brain differences between people who smoke marijuana and people who do not. Such well-intentioned and seemingly objective science is actually a new chapter in a politicized and bigoted history of drug science in the United States.
The study in question compared magnetic resonance imaging (MRI) scans of 20 “young adult recreational marijuana users” (defined as individuals 18 to 25 who smoke at least once a week but who are not “dependent”), to 20 “non-using controls” (age-matched individuals who have smoked marijuana less than five times in their lives). The researchers reported differences in density, volume, and shape between the nucleus accumbens and amygdala regions of the two groups’ brains—areas hypothesized to affect a wide range of emotions from happiness to fear, which could influence basic decision-making.
Researchers did not make any claims about how marijuana affected actual emotions, cognition, or behavior in these groups; instead; the study merely tried to establish that the aggregated brain scans of the two groups look different. So, who cares?
Different-looking brains tell us literally nothing about who these people are, what their lives are like, why they do or do not use marijuana, or what effects marijuana has had on them. Neither can we use such brain scans to predict who these people will become, or what their lives will be like in the future.
Nonetheless the study invented two new categories of person: the “young casual marijuana user” and the young non-marijuana user. This is the latest example of turning to brain imaging to make something seem objective. Establishing brain differences among certain groups highlights the uniquely ignoble political history surrounding the criminalization of a plant.
Marijuana has a particularly frustrating existence in the U.S. There are more people in federal prisons for marijuana offenses than for violent offenses. According to the ACLU, nearly half of drug arrests in 2012 were for marijuana—close to 750,000. And almost half of those arrests were for possession alone. Almost $4 billion is spent annually on the arrest, prosecution, and incarceration of marijuana offenders. And these statistics are egregiously skewed according to race. Police in the biggest American cities like Los Angeles, Chicago, and New York arrest blacks for marijuana possession at a rate seven times greater than their arrest rate for whites, despite that marijuana use rates do not differ between blacks and whites.
Given these injustices, the kind of science that the Harvard study exemplifies offers a cautionary lesson in how neuroscience cannot be an unbiased form of knowledge that, as some posit, “speaks for itself.”
We first started seeing the use of seemingly “objective” metrics to make ultimately social claims about racial inferiority in the 19th century. One clear example of this was the physical anthropology of the mid-1800s, which, among other things, sought to establish race-based theories of “intelligence” and “moral reasoning” based on physical attributes like the shapes of skulls.
Within this tradition, the influential American scientist Samuel George Morton developed “craniometry” in the 1830s to prove that humans were actually made up of separate species, hierarchically ordered in terms of intellectual capacity as determined by skull volumes. Morton’s theories were recruited to justify slavery in the face of growing moral repugnance against it. After his death in 1851, the Charleston Medical Journal eulogized him accordingly: “We can only say that we of the South should consider him as our benefactor, for aiding most materially in giving to the negro his true position as an inferior race.”
It is clear to us now that racist ideology was in play before anyone in the 19th century grabbed calipers and began measuring people’s skulls in the name of scientific inquiry. Yet we do not exactly let 19th-century racist anthropology off the hook because its practitioners adhered to the scientific standards of the time—so why should we treat today’s sciences differently? To what extent is the neuroscience we do today just a technologically-savvy version of a craniometry or phrenology that still reinforces social categories? As the late paleontologist Steven Jay Gould put it, “Shall we believe that science is different today simply because we share the cultural context of most practicing scientists and mistake its influence for objective truth?”
Contemporary neuroscience is being used in the service of today’s dominant culture just as phrenology was used in the service of the dominant culture of a previous era. The neuroscience of illegal drugs is similarly problematic, as it indirectly reinforces historically racist policies against marijuana.
* * *
Neuroscience participates in a sophisticated form of revisionist history: It turns public discourse away from the fact that marijuana is not illegal because it was discovered to cause brain damage, but because of an early 20th-century fear-mongering campaign to associate it with Mexican immigrant workers.
That campaign, infamously led by the first director of the Federal Bureau of Narcotics Harry Anslinger, culminated in the Marihuana Tax Act of 1937—federal legislation that prohibitively taxed cannabis and hemp. Anslinger had also become particularly adept at using public media to propagandize the evils of marijuana. His essay “Marihuana, Assassin of Youth” was published in The American Magazine that same year. In it, Aslinger offered panic-inducing musings like: “How many murders, suicides, robberies, criminal assaults, holdups, burglaries and deeds of maniacal insanity it causes each year, especially among the young, can only be conjectured … No one knows, when he places a marijuana cigarette to his lips, whether he will become a joyous reveler in a musical heaven, a mad insensate, a calm philosopher, or a murderer.”