Thursday, June 21, 2007

Sex differences and cognition

“we have to stop assuming men and women are basically the same because they’re not, which represents a fundamental change in how neuroscience has been doing business-a major zeitgeist change is afoot.”

Larry Cahill, UC Irvine

Although still in its infancy, neuroscience has recently made fascinating in roads into clear differences in neuro processing between the sexes. Using such instruments as fMRI (functional magnetic resonance imaging) and Pet scans to probe the dynamic real time activity of brain function, scientist have discovered unique anatomical and functional differences of male and female brains.

To be clear, men and women on the whole are more similar than they are different. Also, environmental and social conditions likely influence gender neural development in significant ways. The fact remains though that there are real gender cerebral differences that translate into variations in expressed behaviors and cognitive processing. These gender specific differences that can help shed light on subtle male or female cognitive nuances. For example, men tend to use one hemisphere or the other while processing information while relying on specific neural regions to perform tasks. Women tend to utilize broad areas of both hemispheres and multiple regions of the brain to process and perform tasks.

These findings suggest that men and women process information in different ways. An interesting 2005 Harvard fMRI study looking into working memory found that both sexes reached similar results in a working memory test, but used very different neural pathways to get there: “ in a study of working memory-that short-term memory we use to carry on conversations or remembering telephone numbers-a group of volunteers were given verbal attention tasks…while male and female participants performed about the same in terms of accuracy and reaction time, the neural pathways that were activated were different.”

Men and women score similarly in IQ tests even though men’s brains are (factoring in larger proportional size) on average about 100gms heavier than women’s brains. Larger brain size has been correlated with increased intelligence, yet there is no difference in overall cognitive capacity between the sexes.

Studying the make up of each brain reveals a difference in functional emphasis between the sexes. Women have more grey matter and nerve cells more tightly packed together, have a larger superior temporal cortex, and a cerebral blood flow 15 % higher than men, and the prefrontal cortex and temporal cortex are denser. These characteristics suggest that female brains may function more efficiently (making up for their smaller size) and excel in language processing, comprehension, and memory.

Males, on the other hand, have far more white matter-long neuronal fibers coated with a fatty myelin sheath- that enables more efficient communication between distant areas of the brain. In addition, the white matter contains inhibitory neurons that minimize the spread of information throughout the cortex thereby enhancing local processing. This seems to translate into men having an exquisite ability to focus and ignore distractions, as well as being capable of displaying superior spatial reasoning.

These differences likely stem from the ancient conditions of early human social development where men and women filled unique cooperative roles. Perhaps a division of labor brought about by critical survival needs of the species sculpted the neural variations observed in the sexes. Gender differences in cognition may, in part be an inherited evolutionary quality of Homo sapiens.

Another interesting functional difference reflects itself in how the sexes respond to stressful or provocative stimuli. Men utilize the amygdala’s right hemisphere, which is in tune to outside environmental events and communicates with regions that control sight. Women activate the left hemisphere which focuses on the body’s internal environment and is connected to the insular cortex, where sensory information is translated into emotional experiences, as well as the hypothalamus- the command and control for a myriad of physiological activities. Expanding on this Linda Marsa (She Thinks/He Thinks) adds: “the brains right hemisphere distills the essence of a situation, the central idea, while the left side mulls the finer points and tracks the details.”

These findings are just the tip of the iceberg as neuroscience begins to delve deeper into the human mind. It is important to note that these functional differences are general trends in a continuum of functionality between the sexes. As gender roles change and blend into novel situations, our cerebral plasticity in response, will likely adapt and mold these older neural networks in new ways. All the same, these intriguing gender differences help shed light on how and why men and women, though peers, might think a thought in different ways. It illustrates the fact that intelligence and consciousness come in various forms. It also implies that evolution is not done with us!

Ref: Marsa L.She thinks/ He thinks. The brain( Discover) 30-34.Spring 2007

No comments: