فعال سازی مغز در طول بازیابی حافظه اپیزودیک: تفاوتهای جنسیتی
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|33585||2000||14 صفحه PDF||سفارش دهید||5520 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Acta Psychologica, Volume 105, Issues 2–3, December 2000, Pages 181–194
Behavioral studies have shown a tendency for women to outperform men on episodic memory tasks. Here, data from a series of positron emission tomography (PET) studies were analyzed to examine sex differences in brain activity associated with episodic memory retrieval (yes/no recognition). A total of 17 women and 17 men were included in the analyses. The strongest effect of the design was a retrieval-related increase in activity, involving right prefrontal and anterior cingulate regions, that was common to women and men. In addition, a significant task-by-sex interaction effect was observed which involved a distributed set of brain regions, including several frontal areas. These results suggest that while the neural correlate of episodic memory retrieval is largely the same for men and women, some differences do exist. Possible explanations for the observed differences are discussed, and it is concluded that biological and experiential factors jointly contribute to sex differences in brain activity.
Functional neuroimaging studies have identified several brain regions, including prefrontal, medial parietal, medial temporal, and cerebellar regions, whose activity is associated with components of episodic memory retrieval (Cabeza & Nyberg, 2000). Many of the studies that contributed to establish this association included both female and male subjects, suggesting that the activation pattern for episodic retrieval generalizes across gender groups. However, to the best of our knowledge, formal analyses of gender differences in the functional neuroanatomy of episodic memory have not been presented, likely due to limited statistical power to detect gender differences in individual studies. The purpose of the research to be reported here was to use data from a series of positron emission tomography (PET) experiments to explore gender differences in the neural correlates of episodic memory retrieval. We start by presenting a brief review of cognitive studies of gender differences in episodic memory, followed by an overview of functional neuroimaging studies of gender differences in various cognitive domains. In addition to the well-known differences between men and women in visuospatial (men > women; Voyer, Voyer, & Bryden, 1995) and verbal abilities (women > men; Hyde & Linn, 1988), a number of studies have reported that women outperform men in episodic memory tasks (see Herlitz, Nilsson, & Bäckman, 1997). Performance differences have been found from age 5 (Kramer et al., 1997) to age 75 (Herlitz et al., 1997), and are typically smaller in recognition tasks (i.e., effect size d≈16) than in recall tasks (i.e., effect size d≈27; Herlitz, Airaksinen, & Nordström, 1999). The advantage women have over men in episodic memory is evident when the material to be remembered is words (e.g., Kramer, Delis, & Daniel, 1988), stories (e.g., Hultsch, Masson, & Small, 1991), concrete pictures (e.g., Herlitz et al., 1999), faces (e.g., Wahlin et al., 1993), locations ( Eals & Silverman, 1994), and odors ( Lehrner, 1993). No sex differences have been found in recognition of abstract pictures ( Herlitz et al., 1999 and Lewin et al., 2000) and of unfamiliar odors ( Öberg, Larsson, & Bäckman, 2000). This pattern of findings has been taken to indicate that women will outperform men in episodic memory tasks in which verbal processing is required or can be used, whereas no differences between men and women will be found when verbalization of the material is inhibited ( Lewin et al., 2000). Given that women excel in episodic memory tasks in which verbalization is possible, it is possible that this advantage is linked to women's higher verbal ability. However, women do not show higher performance in all verbal tasks, but rather in verbal fluency or verbal production tasks ( Hyde & Linn, 1988). The common cognitive operation in episodic memory tasks and verbal production tasks may be that they require rapid access to and use of information in memory ( Halpern, 1997). Guided by sex differences in behavioral performance, several imaging techniques have been used to study sex differences in the brain's structural and functional organization. This includes analyses of differences in brain anatomy (e.g., Gur et al., 1999), analyses of differences in temporal responses (e.g., Reite et al., 1993 and Skrandies et al., 1999), and analyses of differences in regional cerebral glucose metabolism during rest (e.g., Gur et al., 1995). Of main concern here is analyses of sex differences in hemodynamic responses in cognitive activation studies. Wendt and Risberg (1994) used xenon technology to study cerebral blood flow (CBF) in males and females during rest and three visuospatial tasks. They observed higher global CBF in females than in males in all three visuospatial tasks. However, as females also showed higher global CBF during rest, these data do not constitute evidence for a task-related sex difference in global CBF. Esposito, Van Horn, Weinberger, and Faith Berman (1996) used PET to measure CBF in males and females while they performed three non-verbal neuropsychological tasks linked to prefrontal cortex (Wisconsin Card Sorting, Delayed Alteration task, Spatial Delayed Response Task) and three sensorimotor control tasks, none in which behavioral sex differences could be expected. In agreement with the Wendt and Risberg study, they found that females had higher global CBF than males across the six tasks. More detailed analyses revealed that the effect of sex on global CBF varied across tasks such that it was significant for the neuropsychological tasks, but not for the control tasks. Hence, these findings indicate that gender differences in CBF vary as a function of cognitive state. Buckner, Raichle, and Petersen (1995) used PET to measure regional CBF in males and females while they performed verbal production tasks (stem completion or verb generation) and control tasks. Relative to the control tasks, increased activity was observed in left prefrontal cortex during both speech tasks. This was true for both sexes, but the magnitude of left prefrontal activity during verb generation was greater for males than for females. Shaywitz et al., 1995 (see also Pugh et al., 1996) used functional magnetic resonance imaging (fMRI) to explore sex differences in brain activation while subjects performed various language tasks. When phonological processing was required, male subjects activated left inferior frontal gyrus. By contrast, inferior frontal activation was bilateral for females. Small sex differences in brain activation were also observed in an fMRI study of verbal fluency (Schlösser et al., 1998). In the latter study, similarities in patterns of brain activity for males and females were emphasized, which is in agreement with a recent large-scale fMRI analysis of sex differences in brain activity during a language comprehension task (Frost et al., 1999). A final example comes from a recent fMRI study of brain activation in male and female subjects when they searched the way out of a complex virtual-reality maze (Grön, Wunderlich, Spitzer, Tomczak, & Riepe, 2000). Men and women activated several regions in common, but reliable differences were observed as well. Specifically, men differentially recruited the left hippocampal region whereas women differentially activated right fronto–parietal regions. These differences were seen as differentiating male from female subjects in navigation. Taken together, functional neuroimaging studies of cognitive functions suggest that, although subtle, task-related sex differences in hemodynamic responses exist. Together with documented behavioral sex differences in various cognitive domains, including episodic memory, this pattern of results prompted us to look for sex differences in the functional neuroanatomy of episodic memory retrieval. To ensure reasonable statistical power to detect differences, data from three previous PET studies of episodic memory were aggregated (Nyberg et al., 1995, Nyberg et al., 1996a and Nyberg et al., 2000). Common to all three studies was that they included two conditions which did not put demands on episodic retrieval (baseline/reference conditions), and two conditions that involved yes/no recognition. The type of information (words, sentences, pictures) and the way the information was acquired (incidental/intentional encoding) differed across studies, as did the compatibility between the study and test modality (auditory–visual; visual–visual). What was common across studies was that subjects in all studies were engaged in a retrieval mode ( Tulving, 1983) during the recognition tasks but not during the reference tasks. Retrieval mode has been defined as “a neurocognitive set, or state, in which one mentally holds in the background of focal attention a segment of one's personal past, treats incoming and on-line information as ”retrieval cues“ for particular events in the past, refrains from task-irrelevant processing, and becomes consciously aware of the product of successful ecphory, should it occur, as a remembered event” (p. 506, Lepage, Ghaffar, Nyberg, & Tulving, 2000). Previous studies show that a robust response associated with retrieval mode is increased activity in frontal brain regions ( Cabeza and Nyberg, 2000 and Lepage et al., 2000). Guided by these previous studies, we were especially interested in similarities and differences in brain activity in frontal brain areas for females and males. Moreover, sex differences in imaging studies have been claimed to be particularly prevalent in frontal brain regions (see e.g., Esposito et al., 1996).