Posteromedial Cortex: Pathway to the Self?

PNAS Neural Connections of PMC

One of the interesting aspects of human consciousness is the sense of the "autobiographical self," which provides us with a sense of personal identity and continuity. Recent research at Stanford U. School of Medicine adds new pieces to the human consciousness puzzle, which cognitive scientists are attempting to assemble. They discovered that the posteromedial cortex was extremely active when recalling events in the person's life, but that this activity was shut down immediately when the patient was asked to do a simple arithmetic problem.

The posteromedial cortex is tucked so deeply into the brain that it is often difficult to examine its ongoing function, using traditional imaging tools such s fMRI. In the Stanford study, researchers took advantage of a previously scheduled neurosurgical procedure being done in a group of epileptic patients, using intracranial electrode monitoring of the PMC.

In a study published online Sept. 3 in Proceedings of the National Academy of Sciences, Parvizi and his Stanford colleagues found a way to directly and sensitively record the output from this ordinarily anatomically inaccessible site in human subjects. By doing so, the researchers learned that particular clusters of nerve cells in the PMC that are most active when you are recalling details of your own past are strongly suppressed when you are performing mathematical calculations.

...The researchers took advantage of a procedure performed on patients who were being evaluated for brain surgery at the Stanford Epilepsy Monitoring Unit, associated with Stanford University Medical Center. These patients were unresponsive to drug therapy and, as a result, suffered continuing seizures. The procedure involves temporarily removing small sections of a patient’s skull, placing a thin plastic film containing electrodes onto the surface of the brain near the suspected point of origin of that patient’s seizure (the location is unique to each patient), and then monitoring electrical activity in that region for five to seven days — all of it spent in a hospital bed. Once the epilepsy team identifies the point of origin of any seizures that occurred during that time, surgeons can precisely excise a small piece of tissue at that position, effectively breaking the vicious cycle of brain-wave amplification that is a seizure.

...The experimenters found eight patients whose seizures were believed to be originating somewhere near the brain’s midline and who, therefore, had had electrode packets placed in the crevasse dividing the hemispheres. (The brain’s two hemispheres are spaced far enough apart to slip an electrode packet between them without incurring damage.)

...Significant portions of the PMC that were “tapped” by electrodes became activated during self-episodic memory processing, confirming the PMC’s strong role in recall of one’s past experiences. Interestingly, true/false statements involving less specifically narrative recall — such as, “I eat a lot of fruit” — induced relatively little activity. “Self-judgment” statements — such as, “I am attractive” — elicited none at all. Moreover, whether a volunteer judged a statement to be true or false made no difference with respect to the intensity, location or duration of electrical activity in activated PMC circuits.

This suggests, both Parvizi and Foster said, that the PMC is not the brain’s “center of self-consciousness” as some have proposed, but is more specifically engaged in constructing autobiographical narrative scenes, as occurs in recall or imagination.

Foster, Dastjerdi and Parvizi also found that the PMC circuitry activated by a recall task took close to a half-second to fire up, ruling out the possibility that this circuitry’s true role was in reading or making sense of the sentence on the screen. (These two activities are typically completed within the first one-fifth of a second or so.) Once activated, these circuits remained active for a full second.

Yet all the electrodes that lit up during the self-episodic condition were conspicuously deactivated during arithmetic calculation. In fact, the circuits being monitored by these electrodes were not merely passively silent, but actively suppressed, said Parvizi. “The more a circuit is activated during autobiographical recall, the more it is suppressed during math. It’s essentially impossible to do both at once.” _Parvizi _via SD

As the researchers suggest, the PMC is not likely to be "the centre of self-consciousness." Rather, the PMC is one part of the human brain's mechanism of self-consciousness -- and a crucial part at that.

It is usually a mistake to claim that a specific part of the brain is "the centre" for a specific cognitive or behavioural function. Rather, different brain modules are integrally tied to various behavioural and cognitive functions, and work in concert to perform cognitive and behavioural functions and actions.

PNAS Neural Connections of PMC in Macaque

PLoS One: Functional Connections of the Human PMC

More: CUNY researchers have discovered that androgen receptors in the visual cortex appear to affect how males see the world through their eyes, as opposed to the way that females see the world. Since androgen receptors are scattered throughout the human cerebral cortex, it is likely that male brains not only see the world differently (statistically), but also perceive the world differently in all of their senses, and feel driven to react to what they perceive in a different manner (statistically) than do females.

Bigger and Smarter Brains: What Makes the Difference?

If you look at brain size across the evolutionary tree, it seems clear that larger brained creatures demonstrate greater intelligence, for the most part, when corrected for body size. What is the evolutionary driving force behind increasing brain size?

Researchers found that protein domain called DUF1220 may explain why humans have bigger brains. Humans have more than 270 copies of DUF1220 in their genome whereas chimpanzees have 125, gorillas have 99 and mice have just one. The number of copies of DUF1220 shows how close an animal may be to humans.

"This research indicates that what drove the evolutionary expansion of the human brain may well be a specific unit within a protein – called a protein domain -- that is far more numerous in humans than other species," said Sikela. _Medical Daily

Article abstract
Wikipedia article on "Protein Domain"

Jnl of Cosmology

Something has been driving the evolutionary increase in the size and sophistication of the brain. DUF1220 repeats may well be a part of the story, but are not likely to be the entire explanation.

Besides an increase in overall brain size, the relative size of particular brain components have changed. The frontal lobe size in homo sapiens, for example, is thought to be significantly larger than the frontal lobes in homo neanderthals, while the temporal and occipital lobes were larger in the Neanderthal. So although overall brain size was comparable between the two species of homo, actual brain function would likely have been quite different.

Data from Beals, et al, Oregon State University

Even in the modern extended breeding families (races) of homo sapiens sapiens, we find statistical differences in group brain sizes.

The definitive study of race differences in brain size was carried out on approximately 20,000 crania by Professor Kenneth Beals and his colleagues at Oregon State University. Their results for endocranial volume, measured in cubic centimeters for the major races were as follows: North East Asians (Chinese, Japanese and Koreans): 1,416 cm; Europeans: 1,369cm; Native American Indians: 1,366cm; Southeast Asians: 1,332cm; Pacific Islanders: 1,317cm; South Asians: 1,293cm; Sub-Saharan Africans: 1,282cm; Bushmen: 1,270cm; Australian Aborigines: 1,225cm. These brain size differences correspond with intelligence differences derived from IQ tests given by Prof. Richard Lynn, who finds IQs of 105 for North East Asians,100 for Europeans, and so on downwards to 62 for Australian Aborigines and 54 for the Bushmen of the Kalahari desert. _China Daily Forum

Kenneth Beals PDF Download paper

We find that the gross statistical differences in average brain size appear to correlate with the statistical differences in average IQ.

This would not necessarily be the case, given that changes in the organisation of the brain structures and connections themselves could lead to more efficient brain function. The same is true for changes in molecular and genetic efficiency within brain cells -- a smaller brain does not necessarily mean a less functional brain.

At this time it is best to consider these correlations to be curiosities, rather than reflecting any deeper meaning.

But at least we are slowly stumbling upon some of the answers to our questions. As long as we do not allow our science to be perverted by a misplaced sense of political correctness, we should eventually obtain a fairly clear picture of how larger and more intelligent brains evolved.

How Long Before We Develop a Human Superbrain?

Pharmacological enhancers of cognition promise a bright new future for humankind: more focus, more willpower, and better memory, with applications ranging from education to military combat. Underlying such promises is a linear, more-is-better vision of cognition that makes intuitive sense. This vision is at odds, however, with our understanding of cognition’s evolutionary origins. The mind has evolved under various constraints and consequently represents a delicate balance among these constraints. Evidence of the trade-offs that have shaped cognition include (a) inverted U-shaped performance curves commonly found in response to pharmacological interventions and (b) unintended side effects of enhancement on other traits. Taking an evolutionary perspective, we frame the above two sets of findings in terms of within-task (exemplified by optimal-control problems) and between-task (associated with a gain/loss asymmetry) trade-offs, respectively. With this framework, psychological science can provide much-needed guidance to enhancement development, a field that still lacks a theoretical foundation. _Thomas Hills

The above is the abstract from a recent paper published in Current Directions in Psychological Science, a journal of the Association for Psychological Science, titled: Why Aren’t We Smarter Already: Evolutionary Trade-Offs and Cognitive Enhancements. The authors suggest that we are not likely to develop enhanced intelligence for humans anytime soon, for a variety of reasons. More:

Just as there are evolutionary tradeoffs for physical traits, Hills says, there are tradeoffs for intelligence. A baby’s brain size is thought to be limited by, among other things, the size of the mother’s pelvis; bigger brains could mean more deaths in childbirth, and the pelvis can’t change substantially without changing the way we stand and walk.

Drugs like Ritalin and amphetamines help people pay better attention. But they often only help people with lower baseline abilities; people who don’t have trouble paying attention in the first place can actually perform worse when they take attention-enhancing drugs. That suggests there is some kind of upper limit to how much people can or should pay attention. “This makes sense if you think about a focused task like driving,” Hills says, “where you have to pay attention, but to the right things—which may be changing all the time. If your attention is focused on a shiny billboard or changing the channel on the radio, you’re going to have problems.”

It may seem like a good thing to have a better memory, but people with excessively vivid memories have a difficult life. “Memory is a double-edged sword,” Hills says. In post-traumatic stress disorder, for example, a person can’t stop remembering some awful episode. “If something bad happens, you want to be able to forget it, to move on.”

Even increasing general intelligence can cause problems. Hills and Hertwig cite a study of Ashkenazi Jews, who have an average IQ much higher than the general European population. This is apparently because of evolutionary selection for intelligence in the last 2,000 years. But, at the same time, Ashkenazi Jews have been plagued by inherited diseases like Tay-Sachs disease that affect the nervous system. It may be that the increase in brain power has caused an increase in disease.

Given all of these tradeoffs that emerge when you make people better at thinking, Hills says, it’s unlikely that there will ever be a supermind. “If you have a specific task that requires more memory or more speed or more accuracy or whatever, then you could potentially take an enhancer that increases your capacity for that task,” he says. “But it would be wrong to think that this is going to improve your abilities all across the board.” _MedXpress

Very disappointing, if true. But is it possible that the authors overlooked something? After all, a few million years ago, chimpanzee psychologists and philosophers must have been thinking and saying much the same about the prospects for superior chimp brains, yes?

But in fact, a chimpanzee superbrain did develop, which we call the "human brain."

Despite the minute genetic differences between human brains and their primate relatives, Homo sapiens cognitive ability is significantly more advanced, enabling us to “make complicated tools, come up with complicated culture and colonize the world,” said lead author Mehmet Somel, a postdoc studying human evolutionary genomics at the University of California, Berkeley. Because humans spend more than a decade developing into adults and learning, far more than the two or three years of chimpanzee adolescence, researchers have long suspected that developmental genes are involved in human brain evolution. “And the idea that brain gene expression profiles might be different between species was proposed 40 years ago,” Somel added. _Scientist

We are just beginning to learn the genetic and epigenetic specifics which led to the divergence of the human brain from the brain of the common ape ancestor. Fascinating changes in the details of gene expression in the brain created a whole new level of cognitive functioning. There is no reason to doubt that similar genetic and epigenetic changes could lead to even newer and higher levels of cognition.

The human brain has borrowed various hacks and kludges from brain and nerve evolution all the way back down the evolutionary tree. Some of these hacks and kludges are potentially limiting in terms of other, concurrent hacks and kludges that might otherwise be utilised. But there are potential hacks and kludges which might replace the limiting hacks, and some of these potential hacks might very well allow an entire train of further, enhancing hacks to follow.

That is a possibility that most mainstream psychologists and philosophers fail to understand -- generally because they have adopted groupthink as their modus operandi. This is a common failure of academics from the inbred world of the university culture. Perhaps that is why so many of the world-changing visionaries and billionaires of our day have been high school and college dropouts. They escaped before their brains could be gelded.

There are a number of ways in which we might approach the human superbrain. Simple pharmacologic cognitive enhancers, such as stimulants, are not likely to provide the broad spectrum enhancement we will need. But there are a number of prosthetic enhancements for the human brain which would give us near quasi-superbrain status, over time. Certainly the things that humans can do when empowered by modern computing and telecommunications tools would astound most humans of past eras.

But what we really want, are superbrains that continue working even if the power goes out or the batteries run down. For that, we will need genetic and epigenetic change. So how can we go about inducing these genetic changes without running into the problems that so many highly intelligent persons and breeding groups have run into?

That will be a topic of future articles.

Cross-published from Al Fin the Next Level