This is my main research topic, on which I have been working since July 2005. My project focuses on the neuronal substrates of memory processing, especially the role of the neurotransmitters acetylcholine (ACh) and serotonin (5-HT) in memory. In this project, I am collaborating with Arjan Blokland and Wim Riedel.
Neurotransmitters such as ACh and 5-HT have been shown to be involved in declarative memory, the memory of facts, perceptions, and events. ACh, on the one hand probably affects the storage of information (encoding), whereas 5-HT is likely to be involved in memory consolidation, the translation of short- to long-term memory. ACh and 5-HT are expected to interact in their effect on cognitive functions. However, we do not know the exact nature of this interaction, nor their interactive role in declarative memory.
My project focuses on the interaction between ACh and 5-HT. Is there a synergy between the two, meaning that ACh and 5-HT together have larger effects than those predicted knowing only the separate effects of ACh and 5-HT? Or are they antagonists, suggesting that ACh and 5-HT together affect memory less than predicted from their individual effects? Or is there an effect which is in between the two mentioned above? This is what I want to find out in my project.
In the last two years, I have assessed whether decrements of both ACh and 5-HT simultaneously would impair memory more than the decrease of just a single neurotransmitter. Another study was iniated to examine whether a memory impairment due to decrements in ACh could be reversed by increasing 5-HT. Analysis of both studies is still in progress.
Next to studies with human participants, we perform parallel studies in rats as well. Translational research is important, especially in the development of new drugs to treat memory disorders. I recorded the EEG of the animals during an object recognition task, which assesses object memory, and during elementary auditory and visual stimulus processing. For some results, please go to the animal page.
Next to the interaction, I have also studied the effects of tryptophan depletion alone, which has an effect on 5-HT. First, I performd a mega analysis on results previously obtained by several research groups. Next, I used a new method of tryptophan depletion in order to find out whether this also impairs memory in humans.
