Neuroscience has hit the big time. Every day, popular newspapers, websites and blogs offer up a heady stew of brain-related self-help (neuro-snake oil?) and gee wiz science reporting (neuro-wow?). Some scientists and journalists — perhaps caught up in the neuro-fervor — throw caution to the wind, promising imminent brain-based answers to the kinds of questions that probably predate civilization itself: What is the nature of mind? Why do we feel the way we do? Does each person have a fundamental essence? How can we avoid pain and suffering, and discover joy, creativity, and interpersonal harmony?
While reading a paper on the neuroscience of dreaming I came across a reference to a 1940 paper by Donald Hebb and Wilder Penfield. It’s a neurosurgery case study that is quite stunning. It shows that in some cases, removal of prefrontal brain tissue can actually cause improvements in intelligence and personality. So basically it’s the opposite of the Phineas Gage story.
Here are some excerpts from the paper:
Check out how much was removed!
Hebb, Donald O., and Wilder Penfield. “Human behavior after extensive bilateral removal from the frontal lobes.” Archives of Neurology & Psychiatry 44, no. 2 (1940): 421-438. [link]
I was asked this question on Quora:
From an evolutionary standpoint, why would the early years of brain development be paramount in determining life-long neurological patterns, when those patterns can often be detrimental to long-term success in life?
Good question. We can restate it as follows:
Why would natural selection allow animals to be so sensitive to negative early experience?
I suppose the most important thing to say is that evolution may have nothing to do with this. Natural selection is not the explanation for all phenomena in biology. Some phenomena are the result of purely biophysical processes. In other words, natural selection is not magic — it cannot dissolve biophysical constraints. Natural selection is not an optimizing process — it produces solutions that are “good enough”.
Clearly an organism must have some developmental trajectory in order to become an adult that is capable of passing on its genes. The genetically encoded elements of this trajectory are traits that have undergone the pressures of natural selection. But an organism’s traits are not independent of each other. In other words, there are always going to be trade-offs among traits.
It may be that the long-term consequences of sensitivity in early life are the price organisms — particularly humans — pay for plasticity. One could argue that flexible intelligence is the signature trait of humans, and this requires a great deal of plasticity. One cannot learn about the world if all one’s brain connections are hardwired in the womb. Learning involves being modified by experience — and this requires being sensitive to experience.
So even if sensitivity were a trait that could be selected out, perhaps it doesn’t get selected out because the changes required to achieve steely robustness in the face of adversity might also make us… stupid. 🙂 Or if not stupid, then inflexible and unable to adapt to new circumstances.
And this is not just speculation. My lab has collected some indirect evidence that the most plastic (changeable) parts of the brain are also the most vulnerable to disruption. It is no coincidence that these are the parts of the brain associated with psychiatric disorders — the limbic cortical regions.
I was interviewed by the excellentfor his . Check it out if you want to know about my research… and also my take on the question of Life, the Universe, and Everything. 😛
There’s also a shorter excerpt where we speculate about schizophrenia and “hyperrealities”:
My latest modeling paper has been published in Computational Psychiatry.
Here’s the abstract:
“Schizophrenia is associated with diverse cognitive deficits, including disorders of attention-related oculomotor behavior. At the structural level, schizophrenia is associated with abnormal inhibitory control in the circuit linking cortex and thalamus. We developed a spiking neural network model that demonstrates how dysfunctional inhibition can degrade attentive gaze control. Our model revealed that perturbations of two functionally distinct classes of cortical inhibitory neurons, or of the inhibitory thalamic reticular nucleus, disrupted processing vital for sustained attention to a stimulus, leading to distractibility. Because perturbation at each circuit node led to comparable but qualitatively distinct disruptions in attentive tracking or fixation, our findings support the search for new eye movement metrics that may index distinct underlying neural defects. Moreover, because the cortico-thalamic circuit is a common motif across sensory, association, and motor systems, the model and extensions can be broadly applied to study normal function and the neural bases of other cognitive deficits in schizophrenia.”
Here’s Figure 1, which shows the circuit we modeled.
A very important point about dopamine (DA) and reward, from a recent review paper:
“The DA hypothesis of reward is a ubiquitous feature of the scientific literature, as well as popular media, the internet, and film. Yet, despite the almost automatic tendency of some to explain virtually any aspect of DA function as somehow being dependent on reward, there are critical theoretical and empirical problems with this, many of which have been reviewed in detail elsewhere (Salamone et al., 1997, 2007; Salamone and Correa, 2002, 2012; Floresco, 2015; Nicola, 2016). First and foremost, the term reward has no consistent scientific meaning (Salamone et al., 2005; Salamone and Correa, 2012), and, depending upon the paper, or even the paragraph, this term is used variously to refer to subjective pleasure or hedonic reactivity, appetite, preference, and even reinforcement learning. Given the slippery and imprecise nature of this term, it is wholly inadequate to attribute specific effects in experiments simply to reward without any qualification or explication.” [Emphasis added]
Salamone, J. D., Correa, M., Ferrigno, S., Yang, J. H., Rotolo, R. A., & Presby, R. E. (2018). The psychopharmacology of effort-related decision making: Dopamine, adenosine, and insights into the neurochemistry of motivation. Pharmacological Reviews, 70(4), 747-762.
This post, which mostly provides useful citations, was originally written as an answer to the following Quora question:
I was asked the following question on Quora some time ago:
Here’s my answer: