اثرات تنظیم گلوکز و نظم بر روی حافظه اپیزودیک کلامی در نوجوانان سالم پس از تجویز گلوکز خوراکی
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|33627||2008||7 صفحه PDF||سفارش دهید||6560 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Biological Psychology, Volume 79, Issue 2, October 2008, Pages 209–215
The ingestion of oral glucose has been observed to facilitate memory performance in both elderly individuals and in young adults. However, fewer studies have investigated the effect of glucose on memory in children or adolescents. In the present study, the ingestion of a glucose laden drink was observed to enhance verbal episodic memory performance in healthy adolescents under conditions of divided attention, relative to a placebo drink. Further analyses found that this glucose memory facilitation effect was observed only in adolescents exhibiting better glucoregulatory efficiency. These findings demonstrate that the glucose memory facilitation effect can be generalised to younger individuals. The importance of controlling for treatment order in within-subjects designs investigating the glucose memory enhancement effect is also discussed.
The brain relies upon glucose as its primary fuel (Sieber and Traystman, 1992). In recent years, a rich literature has developed from both human and animal studies indicating that increases in circulating blood glucose can facilitate cognitive functioning (for a review see Messier, 2004). This phenomenon has been termed the ‘glucose memory facilitation effect’ (Foster et al., 1998). It has been suggested that older individuals may benefit to a greater degree from glucose administration, as healthy young individuals are close to their ‘cognitive peak’ (Foster et al., 1998). However, glucose has also been observed to facilitate memory in healthy young adults (e.g. Benton et al., 1994, Foster et al., 1998, Sünram-Lea et al., 2001 and Meikle et al., 2005). A meta-analytic review of the glucose memory facilitation effect has supported the view that verbal episodic memory is the cognitive domain that is most amenable to improvement subsequent to glucose ingestion (Riby, 2004). While an abundant literature now exists suggesting that glucose ingestion can facilitate verbal episodic memory in healthy young adults, it has also been suggested that glucose only reliably facilitates memory in this group of individuals under conditions of divided attention at encoding (Sünram-Lea et al., 2002). Sünram-Lea et al. (2002) administered either a glucose or a placebo drink to healthy young adult participants, before presenting them with a list of to-be-remembered words under one of four ‘divided attention’ conditions. Glucose was observed to facilitate memory recall, relative to placebo, when participants performed a secondary motor task or key tapping task concurrently with word list encoding. However, the authors failed to observe the glucose memory facilitation effect when participants were not required to perform a secondary task, or when cognitive demand was increased by asking participants to recall a longer word list, with target items differentiated by the speaker's gender. By contrast, other researchers have observed that manipulating cognitive load, but not divided attention can induce a glucose memory facilitation effect in healthy young adults. For example, glucose has been demonstrated to enhance performance in these individuals on a difficult serial subtraction task, but not on a serial subtraction task associated with a relatively lower cognitive load (Kennedy and Scholey, 2000 and Scholey et al., 2001). In addition, Meikle et al. (2005) have reported that glucose facilitation of verbal episodic memory for serial position is more reliably observed in younger adults when target lists are longer. It has been further suggested that individual differences in peripheral glucose regulation may alter an individual's sensitivity to glucose enhancement of memory. Glucose regulation is reflected by the phenomenon whereby blood glucose concentration rises for approximately 30 min subsequent to a glucose load, followed by a return to baseline blood glucose concentration—typically within approximately 2 h (Donohoe and Benton, 2000). A link between glucoregulatory efficiency and cognitive functioning has now been well established (Wenk, 1989, Awad et al., 2002 and Messier, 2005). More specifically, it has been reported that glucose cognitive enhancement effects are most profound in older adults with poorer glucose regulation (Hall et al., 1989, Kaplan et al., 2000 and Messier et al., 2003). These findings have also been replicated in younger individuals: young adult males with poor glucose regulation have also been observed to demonstrate superior paragraph recall subsequent to glucose ingestion, relative to ingestion of a saccharin control drink (Craft et al., 1994). In addition, younger individuals with poor glucose regulation have been shown to exhibit inferior performance on a verbal episodic memory task relative to better glucoregulators—an effect that is ameliorated if glucose is consumed prior to memory encoding (Messier et al., 1999). It has been theorised that glucose ingestion is most likely to facilitate memory in younger individuals exhibiting poor glucose regulation, as only in such individuals does blood glucose concentration remain elevated for a sufficient time period to exert a memory enhancing effect (Craft et al., 1994). By contrast, it has been reported that, in older adults, the glucose memory facilitation effect is more pronounced in those individuals exhibiting relatively better glucose regulation (Craft et al., 1994, Messier et al., 1997, Meikle et al., 2004 and Riby et al., 2004). While the effect of glucose on memory has been well investigated in younger and older adults, fewer studies have investigated glucose effects on memory in children and adolescents. Lapp (1981) reported that subsequent to ingestion of a carbohydrate rich meal (which elevated blood glucose concentration), healthy adolescents outperformed a fasted control group of adolescents on a paired-associate learning task. The findings of Lapp's (1981) study may, however, reflect the negative effects of fasting on memory, rather than the positive effects of elevated blood glucose (see Doniger et al., 2006). It has also been reported that attentional capacity benefits from ingestion of a confectionary snack in school children (Busch et al., 2002). Further, the consumption of breakfast has been associated with superior attention and memory in children (Wesnes et al., 2003), an effect that is more apparent subsequent to the ingestion of breakfast meals associated with a slower and more prolonged release of glucose into the bloodstream (Mahoney et al., 2005 and Ingwersen et al., 2007). However, the macronutrient composition of the different treatments used in these studies renders it difficult to infer whether glucose, or other potentially cognitive enhancing nutritional components of these treatments (Gibson and Green, 2002) were responsible for the findings. Therefore, the effect of pure glucose ingestion on episodic memory in healthy adolescents has not been well established. Adolescence is a unique period with regard to brain development (Giedd et al., 1999), and also a time of increased vulnerability for experiencing heightened stress (Byrne et al., 2007). This is relevant, given that stress hormones (i.e. cortisol) are known to impact upon glucose regulation (Plat et al., 1996). While the measurement of stress hormone levels is beyond the scope of the present investigation, it is nevertheless important to establish whether glucose ingestion has a similar effect on memory in this age group compared with other populations in which the glucose memory facilitation effect has been demonstrated. The aim of the present study was therefore to investigate the influence of glucose ingestion and glucoregulatory efficiency on verbal episodic memory in healthy adolescents. In line with previous research conducted with healthy young adults, memory encoding took place under dual task conditions (Foster et al., 1998, Sünram-Lea et al., 2001 and Sünram-Lea et al., 2002). It was hypothesised that oral glucose ingestion would enhance memory for a supraspan word list in healthy adolescents, relative to a sweetness matched placebo. It was further hypothesised that the glucose memory facilitation effect would be observed only in the healthy adolescent participants with poor glucose regulation, in accordance with previous findings indicating that glucose facilitation of memory is observed only in young adults with poor glucose regulation (Craft et al., 1994 and Messier et al., 1999).