Abstract Rationale: Memory for a list of 20 words can be enhanced by preceding learning with consumption of 25 g glucose rather than an equally sweet aspartame so- lution. In previous studies, participants performed a sec- ondary hand-movement task during the list-learning phase. Objective: The present placebo-controlled, dou- ble-blind study examined whether the additional cogni- tive load created by a secondary task is a crucial feature of the glucose memory facilitation effect. Methods: The effect of glucose administration on word recall perfor- mance in healthy young participants was examined un- der conditions where the primary memory task and a secondary task were competing for cognitive resources (across a range of secondary tasks), and where task diffi- culty was increased but dual task-mediated competition for cognitive resources did not exist. Measures of non- verbal and working memory performance were also compared under the different glycaemic conditions (glu- cose versus aspartame drinks). Results: In the present study, a beneficial effect of glucose on memory was de- tected after participants encoded a 20-word list while performing a secondary task, but not when participants encoded the list without a secondary task, nor when the 20 target words were intermixed with 20 non-target words (distinguished by gender of speaker). In addition, glucose significantly enhanced performance on spatial and working memory tasks. Conclusion: The data indi- cate that possible “depletion” of episodic memory capac- ity and/or glucose-mediated resources in the brain due to performing a concomitant cognitive task might be cru- cial to the demonstration of a glucose facilitation effect. Possible implications regarding underlying cognitive and physiological mechanisms are discussed in this article. Keywords Glucose · Short-term memory · Long-term memory · Task difficulty Introduction The past years have seen increasing evidence that mod- est increases in circulating blood glucose concentrations regulate several brain functions, including particularly enhancement of learning and memory. The role of glu- cose in the modulation of central mnemonic processes in both young and aged animals has now been clearly dem- onstrated (Gold et al. 1986; Wenk 1989; Gold 1991, 1992; White 1991). Glucose administration also en- hanced certain aspects of cognitive functioning in heal- thy young humans (Hall et al. 1989; Benton and Owens 1993; Benton et al. 1994; Owens and Benton 1994; Craft et al. 1994; Parker and Benton 1995; Foster et al. 1998; Messier et al. 1998, 1999; Martin and Benton 1999; Metzger 2000; Kennedy and Scholey 2000; Sünram-Lea et al. 2001) as well as in older individuals (Gonder- Frederick et al. 1987; Hall et al. 1989; Craft et al. 1994; Messier et al. 1997). Furthermore, a glucose facilitation effect on cognitive functions has been observed in sub- jects with severe cognitive pathologies, including indi- viduals with Alzheimer’s disease (Craft et al. 1992; Manning et al. 1993), Down’s syndrome (Manning et al. 1998) and schizophrenia (Fucetola et al. 1999; Newcomer et al. 1999). Impairments in certain cognitive skills have also been identified as a possible complication of long- standing, non-insulin- and insulin-dependent diabetes mellitus, and it has been further demonstrated that im- proved glycaemic control can correct for these cognitive deficits (Gradman et al. 1993; Meneilly et al. 1993). Therefore, increases in circulating glucose concentra- tions appear to have an influence on specific aspects of cognitive performance. S.I. Sünram-Lea ( ✉ ) Department of Psychology, Fylde College, University of Lancaster, Lancaster LA1 4YW, UK e-mail: s. sunram-lea@lancaster.ac.uk Tel.: +44-1524-593834, Fax: +44-1524-59344 J.K. Foster Department of Psychology, University of Western Australia, Perth, Western Australia 6907, Australia P. Durlach · C. Perez Unilever Research Colworth Laboratory, Sharnbrook, Bedford MK44 1LQ, UK Psychopharmacology (2002) 160:387–397 DOI 10.1007/s00213-001-0987-9 ORIGINAL INVESTIGATION Sandra I. Sünram-Lea · Jonathan K. Foster Paula Durlach · Catalina Perez Investigation into the significance of task difficulty and divided allocation of resources on the glucose memory facilitation effect Received: 6 August 2001 / Accepted: 22 November 2001 / Published online: 8 February 2002 © Springer-Verlag 2002