Effect of Monday-Thursday Fasting on Working Memory of Adult Human

by:  Dyna Rochmyaningsih
Institution:  Laboratory of Zoology, Bogor Agricultural University, Indonesia
Date:  August 2009

Abstract

Working memory is the ability in the brain to temporarily hold and process acquired information. To perform memory task, human brain needs sufficient glucose pertaining to its energy demand. Thus, fasting, as a temporary condition of no glucose intake into the body, would logically give negative effect on memory performance. This assumption is supported by the finding of untreated patients of hypoglicemia (low blood glucose) that has syndrome of confusion and may have trouble of concentrating. Previous study also showed that overnight and morning fasts produced slower memory recall on schoolchildren in United States and Peru and also for the college students in United Kingdom. It was proposed that metabolic stress and the importance of glucose in the making of acetylcholin were the reasons of the effects. To the contrary, previous study in Indonesia showed that daily fast did not influence the memory of college students but improve the memory performance of teenagers. Thus, following these adverse conclusions, this study aims to find out whether or not fasting influence memory performance of adult human. In this experiment, blood glucose concentration of each subject was electrochemically measured using glucometer while their visual working memory was tested using sequential Delayed Matching to Sample (DMS) task. In this task, subjects were asked to match a number of visual stimuli and the order of its appearance corresponding to the level of the test. To hold the memory of the stimulus, 1500 ms delay period was given in each trial. After 60 trials, data of the reaction time and accomplished level were extracted from the test and would be further analyzed using regression analysis. This test was done in the fasting and the non-fasting conditions for each subject. Result showed that blood glucose level were high around 2.5 hours (110-120 mg/dl), decreased within 6 hours, and then remained constant until 24 hours (80-100 mg/dl). This homeostasis phenomenon was suggested to be the reason why the fasting duration did not influence memory performances both in reaction time and accomplished level. Fasting duration did not significantly influence reaction time with P-value 0.438 in the non-fasting condition and 0.966 in the fasting condition (P>0.05). It also did not significantly influence accomplished level with P-value of 0.432 in the non-fasting condition and 0.642 in the fasting condition (P>0.05). This experiment did not record hunger which was suspected to affect attentional memory processes. Moreover, learning effect and habituation are more considered to affect working memory performance.

The glucocorticoid (GC) known as cortisol is secreted from the adrenal gland when someone is exposed to stress from their internal or external environment. Cortisol modulates various physiological functions during stress to help one adapt; however, it also has an effect on cognitive functions. One cognitive function affected by cortisol, with an increasing interest among scientists, is memory. Various experiments conducted with the goal in mind of finding cortisol's effect on memory, yield contradictory results. Some of the experiments show that cortisol weakens a person's ability to retrieve emotional memory, and enhances their ability to retrieve neutral (Kuhlmann et al., (2005); Tollenaar et al., (2008). Others show cortisol enhances a person's ability to retrieve emotional memory, and impairs their ability to retrieve neutral (M. Jelicic et al., (2004); P. Putman et al., (2004). This review paper focuses on analyzing these experiments and their results, to help expose methodological flaws and, as a consequence, give insight on how to improve future experiments to achieve more valid results. This collective analysis further corroborates the complex functioning of cortisol and how it affects one's ability to recall information of varying emotional valence while undergoing different levels of stress.

In 1997, Stanley Prusiner was awarded the Nobel Prize for his prion hypothesis, which is still used today to describe the propagation of some of the deadliest diseases that affect the central nervous system. However, the prion hypothesis remains controversial, as it does not adequately describe the mechanism by which infection occurs, inheritance of diseases such as CJD, or variations among the infected proteins (i.e. "prions"). I propose a counter argument to the prion hypothesis, the "mutagen hypothesis," to explain the uncertain aspects of pathogenesis of these diseases. This new hypothesis is supported by and explains findings from previous experiments performed by other scientists – findings that the prion hypothesis failed to explain.

In the present study Southern hybridization analysis of Leishmania. donovani gDNA was performed to generate a restriction map of the LdLIP3 gene loci and to determine its copy number in the genome. The gDNA was digested with restriction endonucleases and subjected to agarose gel electrophoresis. Restriction fragments were visualized with ethidium bromide staining and subjected to Southern hybridization with a digoxigenin labeled probe of the full length LdLIP3 gene. Results indicated that the gene is present as single copy. Moreover, our data supports the hypothesis that L. donovani possess a gene that encodes a secreted lipase. To date, there are no published studies concerning the characterization of any lipase genes in Leishmania thus this research provides some of the tools necessary to better understand the role of lipases to the biology and malignance of this important human pathogen.