Further implications of hippocampal theory

So while on my walk today, I got to thinking about various potential implications of the hippocampal theory of time preference.

The short version if you don’t want to read yesterday’s post is that one’s degree of impulsivity/ability to plan / high or low time preference seems to be mediated by an interaction between the nucleus accumbens, which seems to a desire center, and the hippocampus, which does a lot of IQ-related tasks like learn new things and track objects through space. Humans with hippocampal damage become amnesiacs; rats with the connection between their nucleus accumbens and hipocampus severed lose their ability to delay gratification even for superior rewards, becoming slaves to instant gratification.

So, my suspicion:

Relatively strong hippocampus => inhibition of the nucleus accumbens => low time preference.

Relatively weak hippocamus => uninhibited nucleus accumbens => high time preference (aka impulsivity.)

Also, Strong hippocampus = skill at high IQ tasks.

Incentivise traits accordingly.

Anyway, so I was thinking about this, and it occurred to me that it could explain a number of phenomena, like the negative correlation between weight and IQ, eg:

Shamelessly stolen from Jayman’s post. As usual, I recommend it.

(Other theories on the subject: Intelligent people make lots of money and so marry attractive people, resulting in a general correlation between IQ and attractiveness; there is something about eating too much or the particular foods being eaten that causes brain degeneration.)

People generally claim that overweight people lack “willpower.” Note that I am not arguing about willpower; willpower is only a tiny part of the equation.

The skinny people I know do not have willpower. They just do not have big appetites. They are not sitting there saying, “OMG, I am so hungry, but I am going to force myself not to eat right now;” they just don’t actually feel that much hunger.

The fat people I know have big appetites. They’ve always had big appetites. Some of them have documented large appetites going back to infancy. Sure, their ability to stay on a diet may be directly affected by willpower, but they’re starting from a fundamentally different hunger setpoint.

So what might be going on is just a matter of whether the hippocampus or nucleus accumbens happens to be dominant. Where the NE is dominant, the person feels hunger (and all desires) quite strongly. Where the hippocampus is dominant, the person simply doesn’t feel as much hunger (or other desires.)

That a strong hippocampus also leads to high IQ may just be, essentially, a side effect of this trade-off between the two regions.

We might expect, therefore, to see higher inhibition in smart people across a range of behaviors–take socializing, sex, and drug use. *Wanders off to Google*

So, first of all, it looks like there’s a study that claims that higher IQ people do more drugs than lower IQ people. Since the study only looks at self-reported drug use, and most people lie about their illegal drug use, I consider this study probably not very useful; also, drug use is not the same as drug addiction, and there’s a big difference between trying something once and doing it compulsively.

Heroin and cocaine abusers have higher discount rates for delayed rewards than alcoholics or non-drug-using controls

IQ and personality traits assessed in childhood as predictors of drinking and smoking behaviour in middle-aged adults: a 24-year follow-up study (they found that lower IQ people smoke more)

Severity of neuropsychological impairment in cocaine and alcohol addiction: association with metabolism in the prefrontal cortex (Cocaine users are dumb)

HighAbility: The Gifted Introvert claims that 75% of people over 160 IQ are introverts.

Research Links High Sex Drive To High IQ, But Brainiacs Still Have Less Sex Than Everyone Else (Spoiler alert: research does not link high sex drive to IQ. Also, NSFW picture alert.)

I am reminded here of a story about P. A. M. Dirac, one of my favorite scientists:

“An anecdote recounted in a review of the 2009 biography tells of Werner Heisenberg and Dirac sailing on an ocean liner to a conference in Japan in August 1929. “Both still in their twenties, and unmarried, they made an odd couple. Heisenberg was a ladies’ man who constantly flirted and danced, while Dirac—’an Edwardian geek’, as biographer Graham Farmelo puts it—suffered agonies if forced into any kind of socialising or small talk. ‘Why do you dance?’ Dirac asked his companion. ‘When there are nice girls, it is a pleasure,’ Heisenberg replied. Dirac pondered this notion, then blurted out: ‘But, Heisenberg, how do you know beforehand that the girls are nice?'”^[30]” (from the Wikipedia.)

Folks speculate that Dirac was autistic; obviously folks don’t speculate such things about Heisenberg.

Autism I have previously speculated may be a side effect of the recent evolution of high math IQ, and the current theory implies a potential correlation between various ASDs and inhibition.

Looks like I’m not the first person to think of that: Atypical excitation–inhibition balance in autism captured by the gamma response to contextual modulation:

The atypical gamma response to contextual modulation that we identified can be seen as the link between the behavioral output (atypical visual perception) and the underlying brain mechanism (an imbalance in excitatory and inhibitory neuronal processing). The impaired inhibition–excitation balance is suggested to be part of the core etiological pathway of ASD (Ecker et al., 2013). Gamma oscillations emerge from interactions between neuronal excitation and inhibition (Buzsaki and Wang, 2012), are important for neuronal communication (Fries, 2009), and have been associated with e.g., perceptual grouping mechanisms (Singer, 1999).

Also, Response inhibition and serotonin in autism: a functional MRI study using acute tryptophan depletion:

“It has been suggested that the restricted, stereotyped and repetitive behaviours typically found in autism are underpinned by deficits of inhibitory control. … Following sham, adults with autism relative to controls had reduced activation in key inhibitory regions of inferior frontal cortex and thalamus, but increased activation of caudate and cerebellum. However, brain activation was modulated in opposite ways by depletion in each group. Within autistic individuals depletion upregulated fronto-thalamic activations and downregulated striato-cerebellar activations toward control sham levels, completely ‘normalizing’ the fronto-cerebellar dysfunctions. The opposite pattern occurred in controls. Moreover, the severity of autism was related to the degree of differential modulation by depletion within frontal, striatal and thalamic regions. Our findings demonstrate that individuals with autism have abnormal inhibitory networks, and that serotonin has a differential, opposite, effect on them in adults with and without autism. Together these factors may partially explain the severity of autistic behaviours and/or provide a novel (tractable) treatment target.”

This may not have anything at all to do with the hippocampus-NA system, of course.

Schizophrenic patients, on the other hand, appear to have the opposite problem: Hyper Hippocampus Fuels Schizophrenia?:

““What we found in animal models and others have found postmortem in schizophrenic patients is that the hippocampus is lacking a certain type of GABA-ergic [GABA-producing] neuron that puts the brakes on the system,” says Grace. “What we’re trying to do is fix the GABA system that’s broken and, by doing that, stabilize the system so the dopamine system responses are back to normal, so that we can actually fix what’s wrong rather than trying to patch it several steps downstream.””

Wow, I made it through two whole posts on the brain without mentioning the amygdala even once.