Sex differences in memory

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, with fear in particular.

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 but scientific evidence is called into question.[7] As this is a statistical impossibility, this phenomenon then became 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 interactions 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.[8]

Differences may also arise due to opposite sexes having diverse interests and motivations.[9] 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 biases in remembering.[10]

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'.[11]

Recent research suggests that males are more equipped to memorize and recall anything pertaining to spatial awareness.  More specifically, men do better in recalling information with precise metric positional information, or object location.[12]

In a brain activation study,[13] 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

Research suggests that there may be gendered differences in rates of memory decline.  While research on the subject has not always been consistent, it's clear that men and women experience significantly different rates of memory decline throughout their life.

Once menopause begins, a significant number of women begin to notice declines in verbal memory and attention processes.[14] The menopausal transition causes significant hormone changes/imbalances; specifically, estrogen which has been known to impact memory throughout a woman's entire life. When estrogen is on the decline, so is a woman's memory.

It was once decided that the difference in memory decline between genders was due to the typically longer lifespan of a woman, however, this has since been disproven.  The difference between the lifespan of a male and female is not great enough to explain the additional onset of memory decline from disease that woman experience.[15]

Over time, when as much as possible can be held constant, research shows that men are 50% more inclined to experience age related memory loss. Specifically, when it comes to verbal memory, men will experience significantly greater memory decline than women.[16] Verbal memory[17] refers to memory of words and other abstractions involving language.

Alzheimer's Disease

As men and women age, dementia become more likely to manifest. Dementia has been reported to affect up to 5% of people over the age of 65. Of the different types of dementia, Alzheimer's Disease is the most common, accounting for up to 65% of dementia cases.[18] Research into the disease is ongoing, but there appears to be evidence supporting the claim that Alzheimer's manifests differently between the sexes.

Multiple studies have found that there is a significant difference in the symptoms of Alzheimer's Disease that affect the sexes. Some of these Behavioral and Psychological Symptoms of Dementia (BPSD) include depression, anxiety, dysphoria, nighttime disturbances, and aggression. Several recent studies have found that women tend to exhibit symptoms such as depression and anxiety more often than men.[19][20][21][22] One study has even gone as far as to suggest that having depression at any point during midlife increases chances of Alzheimer's Disease developing later by up to 70%.[21] Men, on the other hand, exhibit symptoms such as aggression and other socially inappropriate behaviors more often. In addition, it has been found that men are more likely to have coronary artery disease which has been known to damage the blood brain barrier (BBB) by causing micro vascular lesions. Damage to the blood brain barrier seems to be connected to cognitive decline and several forms of dementia, including Alzheimer's Disease.[22] There are many other factors that may determine the frequency or severity of symptoms between the sexes. For example, a male may show more aggressive tendencies because of genetic predisposition, higher levels of testosterone, or learned behaviors through social interactions.[20]

Another contributing factor to differences in Alzheimer's progression between the sexes may be socioeconomic status (SES). Men, historically, have had better opportunities to obtain an education and increase their SES. In recent years, women are being afforded many of the same opportunities, which may explain why there appears to be a decrease of instances of dementia in women that are related to SES factors.[21]

While the differences in observable symptoms for men and women appear to be significant, treatment for Alzheimer's Disease does not show any tendency to work better for one sex over the other.[19]

References

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