Monday, March 27, 2006

Cognitive Sex and Gender Differnces

While the scientific findings that male and female brains are anatomically and functionally different, statistically, is still quite controversial on a political level, on a purely scientific level it is becoming well established. Doreen Kimura is one of several prolific women cognitive scientists who are brave enough to buck the political storm in order to pursue scientific truth. Camilla Benbow is another.

In this article published in Sexualities, Evolution and Gender, Kimura plainly lays out the basic argument and evidence.

Many reliable anatomical brain differences have been found to differentiate men and women, from basic structures such as the hypothalamus, to differences in systems connecting the two hemispheres, such as the anterior commissure. Some of these have been reviewed in my book......We don’t yet know the significance of such differences for cognitive function, but to describe them as fiction is to deny the careful investigations of many respected scientists (e.g., Allen and Gorski 1990, 1991; Allen, Hines, Shryne and Gorski 1989; Allen, Richey, Chai and Gorski 1991). Although we now have a fair understanding of how brain systems work in mediating certain cognitive functions such as memory, language, and the like, we are still far from understanding how individual differences, the variation in such functions from one type of person to another, are mediated by the brain. However, it must follow that if two groups (such as males and females, left-handers and right-handers, or masculine and feminine gender types) differ reliably in some behaviour not simply dependent on physical differences, then their nervous systems must also differ in some way. Where else could the behavioural differences reside? This is just as true of learned as of unlearned behaviours. Brain differences underlying cognitive differences need not, however, be visible in simple structural features. They may take the form of differing organizational mechanisms not apparent by simply viewing the external brain.

This Scientific American article by Kimura presents the argument more methodically, and at greater length.

Men and women differ not only in their physical attributes and reproductive function but also in many other characteristics, including the way they solve intellectual problems. For the past few decades, it has been ideologically fashionable to insist that these behavioral differences are minimal and are the consequence of variations in experience during development before and after adolescence. Evidence accumulated more recently, however, suggests that the effects of sex hormones on brain organization occur so early in life that from the start the environment is acting on differently wired brains in boys and girls. Such effects make evaluating the role of experience, independent of physiological predisposition, a difficult if not dubious task. The biological bases of sex differences in brain and behavior have become much better known through increasing numbers of behavioral, neurological and endocrinological studies.

Read the entire article here, it is quite fascinating.

This is a brief list of scholarly research supporting the concept of "innate differences" in neuroanatomy and cognition in males and females. It is a very abbreviated list, but it serves to introduce the evidence. For a much longer list, consult this reference list from one of Kimura's articles. Scroll down to the list, and continue scrolling. There are 111 citations, and that list is far from complete.

I have posted on this topic before--here, here, and here.

The research continues, and the weight of research--new and old--points to significant cognitive sex differences, or if you prefer, gender differences or gender disparities.

Politically, this is not a popular topic, and politically inclined "scientists" will more easily cling to the political line. It is difficult to get funding for this type of research, and publishing in some mainstream journals is difficult. Even university presidents can fall from grace if they forget the politically correct stance, and deviate from it. This has not discouraged the very persistent women and men of cognitive science.

Neither men nor women are superior to the other as groups. Both groups have statistical strengths and weaknesses. A wise society will seek to understand its members, rather than try to sweep under the rug any scientific findings that are inconvenient to a dominant political viewpoint.

Addendum: This Guardian article by Simon Baron-Cohen contains a link to a test you can take to determine if you have a male brain or a female brain. Just looking at your genitalia or your chromosome map will not tell you that. Regardless of your chromosomes, your brain has a mind of its own, perhaps of a different gender than your body. Are you willing to find out?

Gender Difference: The Gap that Will Not Close

At the elite levels of sports and athletics, the gender gap is prominent and resists closure. There is an approximate 15 minutes difference in the best times of elite male marathoners, and elite female marathoners. Other sports show similar differences at the elite level.

Remember when it was predicted that intensive training for women in athletics would close the gender gap in performance? Some years ago, when the marathon was first becoming a competitive event for women, the rapid improvement in female times led some to predict that female performances would soon equal those of men in the marathon. This has not happened, and it won't. The current world record for women is 2:21, compared to 2:06:50 for the men, a difference in speed of about 10%. This same 10% gap is present across the distance running performance spectrum The reason for the performance gap is not that women don't train as hard as men. There are some important physiological differences between the sexes that can't be overlooked or overcome.

....The "typical" young untrained male will have an absolute VO2 max of 3.5 liters/min, while the typical same-age female will be about 2 liters/min. This is a 43% difference! Where does it come from? Well first, much of the difference is due to the fact that males are bigger, on average, than females. Us humans are all (sort of) geometrically similar, so heart size scales in proportion to lean body size . If we divide VO2 by bodyweight, the difference is diminished (45 ml/min/kg vs 38 ml/min/kg) to 15 to 20%, but not eliminated.

....It is important to make note of the fact that these differences are "on average". In reality, there are many women with significantly higher VO2max values than average men. However, if we look at the "best of the best", the differences persist. Using XC skiing as an example from here in Norway, the highest reliable values for VO2 max recorded in national team XC skiers are about 90 ml/min/kg. The very best Norwegian woman has been measured at 77 ml/min/kg, a 17% difference. So, while this woman will outperform 99.9% of all men, she will not out-perform the national team level males.

Read more here.

A number of studies have demonstrated that boys inherit a performance advantage in athletics, for both pre-puberty, and even more so in post-puberty.
The stopwatch does not lie, and whether in swimming, running, weightlifting, shot put, bicycling etc. the superior VO2 max and muscle mass of males prevents the gender gap in athletics from closing. The only way to narrow the gap is to train the elite athlete girls and confine the elite athlete boys in restraints to encourage muscle atrophy and loss of VO2 max.

In the cognitive realm, you see a similar phenomenon in the measures of spatial ability and mathematical ability at the elite levels. Although hope springs eternal that training will narrow the gap, as in athletics, sometimes it seems that the only way to narrow the gap is to train the elite girls and prevent the elite boys from training somehow.

One can be excused for wondering why all the excitement about male superiority in a small area of elite cognitive performance? The number of jobs involved is minimal. Certainly an intelligent businesswoman, female physician, or female lawyer, can make much more money than an elite mathematician, physicist, or engineer. What is all the near-hysteria about?

Average intelligence levels of men and women test virtually identical. A 1995 study examined the performance of more than 100,000 American adolescents on various mental tests. The study found that on average, females performed slightly better than males on tests of reading comprehension, writing, perceptual speed, and certain memory tasks. Males tended to perform slightly better than girls on tests of mathematics, science, and social studies. In almost all cases, the average sex differences were small.

And here is how developmental psychologist David C. Geary puts it:

There was no sex difference on the IQ test, but males showed significantly higher mean scores on the arithmetical computations, arithmetical reasoning, and spatial cognition measures. A series of structural equation models indicated that individual differences in arithmetical reasoning were related to individual differences in IQ, spatial abilities, and computational fluency. Moreover, the results suggested that the male advantage in arithmetical reasoning is mediated by the male advantages in both computational fluency and spatial cognition.

Women are graduating from schools of higher education at a rate of 6 to 4 vs. men. Women have achieved virtual parity in schools of medicine and law, and make up about 70% of graduate psychologists. Women are achieving phenomenally in the modern world, and if any gender should be worried about current trends, it is the males. A few men are holding on under siege, to a small sliver of cognitive excellence, and all that many psychologists can think of doing is to try to eliminate the small gap within that tiny sliver of cognitive performance.

It is a fascinating study in academic frustration--the data will simply not behave in a politically correct fashion. Many more research studies and outreach programs will be mandated, however, to erase that gap. But I can tell the gender psy-sers exactly how to erase the gap, and I will not charge for the valuable information. Simply prescribe pro-androgenic drugs that cross the placental barrier, to pregnant women in their second trimester, who are carrying female fetuses. Some additional androgenic supplementation may be necessary at different time periods after birth--and there will be potentially unpleasant side effects. Hirsutism, deep voice, skin blemishes, a certain manly aggressiveness, etc. But all of that would be a small price to pay to erase the gender gap in this one small remaining area of academics, no?

Just as there are elite women athletes who can defeat 99% of males in their sport, there are women mathematicians and physicists who are better at their trade than 99% of males. But they are not competing against those 99%. They are competing against the elite males, a very small number, but a significantly greater number than the number of elite females in those vocations. That is the hump that the gender Procrusteans are incapable of leveling. The relatively tiny number of male elites in a relatively tiny number of fields who will simply not go away.

Lawrence Summers paidwith his job, for making a very timid suggestion about possible biological gender or sex differences in that very small, elite sliver of academic professorship in a few top rank schools. The politics of this subject are absolutely deadly to anyone in a public position who lets down his guard for even a moment.

But why? I will deal with the real reasons for the excitement in a later posting.

DNA Surprises: Genetic Research in High Gear

Thanks to Snowcrash for pointing to this CIT newsrelease that details new discoveries in "gene interaction."

The difficulty lies in the fact that two genes can pair up in a gigantic number of ways. If an organism has a genome of 20,000 genes, for example, the total number of pairwise combinations is a staggering total of 200 million possible interactions.

Researchers can indeed perform experiments to see what happens when the two genes interact, but 200 million is an enormous number of experiments, says Weiwei Zhong, a postdoctoral scholar at the California Institute of Technology. "The question is whether we can prioritize which experiments we should do in order to save a lot of time."

....a genetic-interaction network provides a faster and better way at determining how certain genes interact. Such a network also provides information about whether anyone has ever done an experiment to determine the interaction of two particular genes in one of several species.

"This process works like a matchmaking service for the genes," says Zhong. "It provides you with candidate matches that most likely will be interacting genes, based upon a number of specified features."

The benefit, she adds, is that biologists do not need to do a huge number of random experiments to verify if two genes indeed interact. Therefore, instead of the experimenter having to run 20,000 experiments to see if two genes randomly chosen from the genome of a 20,000-gene organism interact, they might get by with 10 to 50 experiments.

"The beneft is that you can be through in a month instead of years," says Sternberg
Read the entire report here. Hat tip Biosingularity Blog.

The next story deals with advances in developing transgenic plants--getting plants to make proteins from other species--in this instance getting tobacco plants to make human albumin. This is from a newsrelease:

Agricultural engineer, Alicia Fernández San Millán, has developed a novel technique in Spain - plastidial transformation, in order to produce, in a recombinant form, human albumin from tobacco plants. According to her PhD thesis, plastidial transformation is an economically viable alternative, as it enables increasing the levels of HSA by between 10 and a 100 times, compared to levels obtained by nuclear transformation. Read the entire newfeature for more information.

The following story deals with "junk DNA", the 98% of all human DNA that does not code for protein. Buried within the junk DNA is hidden treasure--epigenetic control sequences that influence the gene expression of the 2% of coding DNA.

The notion that mutations in enhancers play a role in human disease progression has been difficult to confirm because usually enhancers are located in the 98 percent of the human genome that does not code for protein, termed non-coding DNA. Unlike DNA sequences that code for protein, non-coding DNA, sometimes referred to as "junk" DNA, follows few rules for organization and sequence patterns and therefore is more difficult to study.

"The difficulty with human genetic approaches to common disease is that we lack the power to precisely localize DNA sequences that are associated with disease, often leaving us immense stretches of DNA to look at," says one of the study's corresponding authors, Andy McCallion, Ph.D., an assistant professor in the McKusick-Nathans Institute. Most often one is limited to looking in the most obvious places, which may not yield the best results. "Until now," he says, "we've only been able to look under the lamplights for the car keys."

....The system is a significant advance over current methods in this model species, allowing researchers to study more sequences in a shorter period of time.
Read the entire news report here.

This report discusses a discovery of a gene variant--always think "hapmap" when hearing the term "gene variant"--that affects the onset of cancer.

Normally our genes have to be divided into two perfectly identical copies when a cell divides. The unfortunate variant causes a defect in the division of the genetic material (mitosis), which means that a daughter cell may get too few or too many genes.

If a daughter cell does not receive a gene that prevents cancer, a so-called tumour suppressor gene, then a cancer can grow. One defence mechanism against cancer is for a cell that gets faulty genes to commit suicide (apoptosis).

The defect caused by the unfortunate variant when it divides the genes is so tiny that the suicide mechanism does not detect the fault, which allows the cell to continue its growth into a cancer.
Read the rest here.

Finally, here is a glimpse into the distant past, toward the possible origin of life on earth. This Eurekalert newsrelease discusses experiments attempting to delve into possible origins of the DNA-RNA encoding system that supports all known life.

This "evolutionary conversion" provides a modern-day snapshot of how life as we understand it may have first evolved out of the earliest primordial mix of RNA-like molecules-sometimes referred to as the "pre-RNA world"-into a more complex form of RNA-based life (or the "RNA world") and eventually to cellular life based on DNA and proteins. Nucleic acids are large complex molecules that store and convey genetic information, but can also function as enzymes.

While the transfer of sequence information between two different classes of nucleic acid-like molecules-between RNA and DNA, for example-is straightforward because it relies on the one-to-one correspondence of the double helix pairing, transferring catalytic function is significantly more difficult because function cannot be conveyed sequentially. The present study demonstrates that the "evolutionary conversion" of an RNA enzyme to a DNA enzyme with the same function is possible, however, through the acquisition of a few critical mutations.

The study was released in an advance online version of the journal Chemistry & Biology.
Read more here.

This posting covers only a small cross section of ongoing genetic research. Al Fin has covered several of these topics previously. All of those past postings are available via the archives on the sidebar. Most people would feel overwhelmed if they had attempted to look deeply into any of these reports. No one is expected to know everything about everything, after all.

Saturday, March 25, 2006

How to Search This Blog

Often, a google search will land you at a website such as this for no apparent reason. Your search terms apparently have nothing to do with the current postings. Do not give up yet. First, use the blogger search tool at the top of the page. Place your search terms in the window, and click on "search this blog." Then if there are any postings anywhere on this blog that match your search terms, they will be displayed on the search results page.

If the webpage has an added google search bar, you can also do a google website search, which is very much like a blogger website search, if not identical.

Friday, March 17, 2006

Memory Theory from Develintel

Chris Chatham of Developing Intelligence Blog has a dynamite posting today on "Visualizing Working Memory." Chris finds that the conventional view of human memory as pictured above, is deficient in several ways, that he details in his post.

Although hugely influential, the model has a few unfortunate shortcomings.

Most importantly, memory is not a static process. Memory decays unless it follows the cycle of learning, encoding, recall, and recoding. In contrast, the classic "modal" model distinguishes storage functions from processing functions - i.e., one is a "black box" and one is a "black arrow." Unfortunately, this distinction is artificial, because the brain contains only arrows: processing (activation) and memory (synaptic efficacy) are two sides of the same coin, and memory itself is a process.

Second, all arrows are not created equal. "Architectural" differences (such as the synaptic efficacy of recurrent connections) among different parts of the brain lead to different processing profiles. These profiles can differ in terms of bandwidth, or in other words, how much information they are capable of holding at a time. Orthogonal to bandwidth, these profiles can also differ in terms of decay rate (or alternately, vulnerability to interference): that is, some regions are capable of maintaining information indefinitely while others are capable of maintaining memories for less than one second.

Third, multiple processing paths require gating functions. Perhaps the largest advantage of removing the "boxes" from the traditional "box and arrow" diagram is that one must become explicit about the functions performed at every step. As a result, such diagrams will be more likely to provide a nice one-to-one relationship between cognitive functions and neuroanatomy. And pure-arrow diagrams remove the need for some elusive "executive functioning" box to coordinate and configure the processes; instead, one need only posit a gating function at the intersection of every arrow with another, in which some process allows information to pass along from one arrow to the next (probably based on dopamine fluctuations).

Then Chris describes his own developing model of memory, which is pictured below and to the left. He has drawn his own model to better reflect the physiological realities of memory as he has discovered them to be.
Sensory Memory. As you can see from the image ...., incoming sensory information has an extremely high initial bandwidth, and a rapid rate of decay, as indicated by the fat, short arrows. Furthermore, there is no rehearsal process, and sensory memory is constantly overwriting itself. This is indicated visually by the multiple arrows which overlap, and quickly diminish in width.

Working Memory. This process slowly transitions into a relatively low-capacity - and low-decay - polymodal short-term/working memory process, as indicated by the smaller width of the arrows in the middle of the diagram. Importantly, the width of this arrow does not shrink over time, indicating that the rate of decay is extremely low; indeed, we can hold somewhere between 4 and 7 items in working memory (depending on modality) without decay.

This short-term/working memory process feeds two unique rehearsal processes, each of which is relatively robust to decay yet limited in bandwidth: an articulatory rehearsal process, as well as an "inner scribe" which supports imagery functions (such as mental rotation). These rehearsal processes essentially "refresh" short-term/working memory with previous information, allowing it to be maintained over time.

Long Term Memory. Finally, the entire diagram rests above the base of one massive arrow that folds back on itself: this represents long-term memory. Long-term memory has an essentially unlimited capacity, as indicated by this arrow's enormous base width, but is subject to decay and interference over time. Items can be retrieved from long-term memory, at which point a "gating function" permits us to actively think about the past (i.e., rehearse it), or to merely let it recur and disappear again from our "mind's eye."

Read the entire article here.

I am not surprised that Chris has referred to work from Gerald Edelman's lab in previous posts. This model reminds me of some of Edelman's concepts of memory, as described by Rosenfeld in The Invention of Memory. Chris has some very impressive postings on his blog. Be sure to look through them.

Monday, March 06, 2006

For a Neuron, Too Much Excitement Can Kill

We know that much of the damage from strokes comes from an overload of glutamate, an excitatory neurotransmitter. Neurodegenerative changes in Alzheimer's Disease is probably also due to glutamate overexcitation, at least in part. Now scientists are beginning to tease apart the mechanism of excitative neurotoxicity. This news release give more information:

For neurons, overexcitement is deadly. To avoid this, brain cells must sop up unneeded neurotransmitters from the synapse through membrane-bound transporters. If these transporters fail, neurons and other brain cells get excited to death-- a phenomenon that may contribute to brain damage during stroke and Alzheimer's disease.

Indeed, brain deterioration after stroke is associated with elevated levels of glutamate -- the major excitatory neurotransmitter in the mammalian central nervous system (CNS) -- in the plasma and cerebral spinal fluid. One possible explanation for this glutamate build-up, reported online on March 6th in The Journal of Experimental Medicine, is a mutation in the gene encoding the glutamate transporter protein EAAT2.

This mutation --- a single nucleotide change in the promoter region of the EAAT2 gene -- was equally prevalent in healthy individuals and stroke patients. But among stroke patients, those with the mutated allele had higher plasma levels of glutamate and were more likely to suffer from post-stroke neurological problems than those with the normal allele.

The mutation changed a binding site for the activating transcription factor AP-2 into a binding site for the repressor GCF2 -- a swap that inhibited promoter activity in transfected rat brain cells. Whether the mutant promoter decreases EAAT2 expression in the human brain, as would be predicted, remains to be tested.

Little by little, gene by gene, protein by protein, science is learning why humans suffer the way they do. And little by little science is finding ways to do something about it.

New Research Brings Artificial Organs Closer to Reality

Tissue engineering has long been in need of biological "fill material." Blood vessels, nerves, and other small structures lie in a "matrix" of tissue that supports it and facilitates necessary growth of biological structures. A recent news report details the creation of a new type of "bio-gel" that may suit the need.

Scientists at The University of Manchester have created a new type of 'bio-gel' which provides a pH neutral environment for culturing cells in 3D, as published in the journal Advanced Materials (March 2006).

The gel is the first pH neutral material made from combinations of dipeptides (pairs of amino acids) to provide an environment in which cells can be cultured under physiological conditions.

Uniquely, the gel mimics the properties of cell scaffolds which naturally occur in the body and has potential applications for wound healing and tissue engineering.

Cell scaffolds, known as the extra cellular matrix (ECM), are naturally produced by the body to grow new cells in order to repair damaged tissue. Like the ECM, the gel acts like a scaffold in which cells can grow.

In their paper, 'Nanostructured Hydrogels for Three-Dimensional Cell Culture Through Self-Assembly of Fluorenylmethoxycarbonyl-Dipeptides', Dr Rein Ulijn and collaborators describe how the gel is created through a process of self-assembly.

Dr Ulijn said: "We have used combinations of modified dipeptides which act like building blocks and spontaneously assemble into nanometer sized fibres when exposed to physiological conditions, to create a fibrous gel-like structure in which cells can be cultured. Because this material is made up of 99% water and is pH neutral, it is compatible with biological systems.

"By using dipeptide building blocks instead of much larger oligo-peptides used by other researchers, we have greater control over the fibrous architecture and the physical properties of the gels. These materials offer us great potential for future applications in wound healing and regenerative medicine."

Dr Ulijn and his collaborators have successfully cultured cartilage cells using the gel. They found that both the properties of the gels formed and the cell response to the gels could be controlled by using different combinations of di-peptides. The team recently received a £630k award from EPSRC to develop the gels further.

This is good news for tissue engineers, and forward thinking plastic surgeons. With improvements in collagen synthesis, cartilage production, and other basic level tissue engineering processes, the creation of functioning lab-grown organs, complete with support tissue, is much closer.