Sex differences in memory

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Although there are many physiological and psychological gender differences in humans, memory, in general, is fairly stable across the sexes. By studying the specific instances in which males and females demonstrate differences in memory, we are able to further understand the brain structures and functions associated with memory.

It is within specific experimental trials that differences appear, such as methods of recalling past events, explicit facial emotion recognition tasks, and neuroimaging studies regarding size and activation of different brain regions. Research seems to focus especially on gender differences in explicit memory. Like many other nuances of the human psyche, these differences are studied with the goal of lending insight to a greater understanding of the human brain.

History of research

Perceptions of gender differences in cognitive abilities date back to ancient Greece, when the early physician Hippocrates dubbed the term 'hysteria' or 'wandering womb' to account for emotional instability and mental illness in women.^[1] This diagnosis survived up until the mid-19th century and the beginning of the women's suffrage movement, and was used as evidence for women's inability to handle intellectual work.^[1] Prominent physicians of this era, including neurologist Sigmund Freud, argued that women were biologically suited to homemaking and housework, as they did not have enough blood to power both the brain and the uterus. When women began attending university in the late 19th and early 20th centuries, opponents asserted that the high demands of post-secondary education on the female brain would render women sterile.

The mass entrance of women into the workplace during World War I to replace the conscripted men fighting overseas, provided a turning point for views on women's cognitive abilities. Having demonstrated that they were capable of functioning in the workplace, women gained the right to vote in post-war United States, Canada and the United Kingdom. Though women were able to vote and hold paid employment, they were still not regarded as intellectually equal to men. The development of the encephalization quotient by Harry Jerison in 1973 seemed to confirm popular beliefs and about women's cognitive abilities; this quotient was one of the first means of indirectly measuring brain size, and it demonstrated that women have, on average, smaller brain areas than men.^[2] Modern neuroscience has since demonstrated that women compensate for their smaller brains with increased neuronal density, and there are no significant differences in mean cognitive abilities between men and women. Recent advancements in neuropsychology and cognitive psychology have shown, however, that specific differences in cognition - including memory - do exist. There is an ongoing debate about the causes of those differences, with biology, genetics, culture, and environmental factors all likely contributing.

Explicit memory

When participating in a facial emotion recognition task, explicit memory is used. The knowledge of what a face looks like in various emotional states is something that is learned and stored in memory. It is found that women are typically more sensitive to emotional recognition tasks than men.

In a study which assessed identification of emotions on faces^[3] (happiness, sadness, fear, anger, disgust, or neutral) females excelled at the explicit identification of emotions, especially fear and sadness. Women are better than men in general at explicit emotional recognition, but especially so with the negative emotions.

Based on brain imaging studies, women also show heightened neural sensitivity to negative emotions compared to men. In addition, women are postulated to have larger orbitofrontal regions which are involved in emotional regulation. This may contribute to heightened accuracy in the facial emotion recognition task, as well as more accurate identification of emotionally laden content.^[3]

However, in another study, females showed no difference in remembering details from affective passages versus neutral passages, while men showed more recall for the affective passage.^[4] Female recall was stable, and consistent to men's overall levels, which indicates that women are generally more attentive to remembering verbal passages, and men only become more attentive when the passage has highly emotional content.

Lastly, women show an own sex bias in remembering gendered faces. Females exceed males at facial recognition for other female faces, but not for male faces.^[5]

Semantic verbal fluency is another aspect of explicit memory. A verbal fluency test checks ability to recall facts about the world, and general knowledge such as vocabulary. When asked to list words that start with the same letter or are in the same semantic category, women are able to produce more words than men. This is most likely due to differing styles of recall. Women tend to have a more even balance between clustering (generating words within subcategories) and switching (shifting between clusters) which allows them to come up with more words. Men switch categories less often and tend to make clusters with more words in them. This is not as efficient a strategy as the one generally employed by women.^[6] This provides evidence that while there are differences in the sexes verbal fluency abilities, it could be due to differing recall strategies as opposed to major differences in actual semantic knowledge.

Recall strategies and memory

The examinations of the differences in recall strategies between males and females originated with studies of sexual behavior. In some studies, men reported, on average, to having had more heterosexual sexual partners than women had. As this is a statistical impossibility, this phenomenon then became of the focus of studies, some of which examined the hypothesis that this was due to a gender-based deficiency in memory, and recall into gender based recall strategies followed.

One experiment into the recall strategy of the number of a persons sexual partners has found differences, between the genders. Males were observed to most often attempt to estimate their number of sexual partners, which in some cases led to overestimation, while the women studied generally attempted to list all of the partners they have had, which due to the potential of forgetting an incident, in some cases led to underestimation.^[7]

Differences may also arise due to opposite sexes having diverse interests and motivations.^[8] For example, in a study testing recall of sexual versus non-sexual television advertisements, men were found to recall sexual advertisements better than non-sexual ones. This effect increased when sexual advertisements were embedded in sexual programming. Women, however, were equally good at remembering sexual and nonsexual advertisements. Differing levels of interest in the two types of commercials may explain the gender baises in remembering.^[9]

Short-term memory

Females have been shown to have consistently stronger short-term or working memory than men. Women are thought to be able to hold more items of verbal information in short-term storage at once. This advantage in short-term memory is thought to be linked to women's superior ability to attend to more than one task at once, or 'multitask'.^[10]

Recent research suggests that men have advantages in specific subtypes of short term memory, specifically those pertaining to visuo-spatial information.

In a brain activation study,^[11] working memory tasks showed more bilateral activation in male brains versus overall left hemisphere activation in female brains. This provides evidence that different brain structures may be responsible for short term memory differences in males versus females.

Memory loss

There may be gendered differences in rates of memory decline. Though research on the subject has not always been consistent, it is known that women experience much higher rates of Alzheimer's disease. This difference in rates was initially attributed to women's typically longer lifespans, but the relatively small difference in years of life has been found to be insufficient to explain the incidence of a disease that occurs over decades. Recent research has suggested a link between menopausal declines in estrogen and inefficiencies in brain metabolism. A lack of female hormones may decrease the energy efficiency of brain cells, causing the brain to have inadequate fuel and experience subsequent cognitive decline. Clinical trials of hormone replacement therapy have not shown to be effective at preventing the disease. This area would require further investigation to understand the differing Alzheimers rates between genders.

The prognosis of Alzheimer's disease also differs between men and woman. Though women tend to experience a much sharper decline in grey matter at the onset of the disease, men catch up and eventually overtake women in grey matter loss as the disease progresses.

General age-related memory decline also varies by gender. When all factors, such as age, education, socio-economic status and geographic location are held constant, men are found to be at a 50% increased risk of experiencing significant age-related memory decline.^[12]

References