Serotonin and attention

Edgar, Christopher James (2007) Serotonin and attention. Doctoral thesis, Northumbria University.

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Abstract

The serotonergic system along with other brain neurotransmitter systems has been implicated in the modulation of cognitive function. Dysregulation or pathology in neurotransmitter systems is thought to underlie the cognitive impairments associated with normal ageing, a number of disease states and chronic drug abuse. Research into the influence of serotonergic systems on cognition has focussed on the modulation of other neurotransmitter systems by serotonergic input and the importance of serotonergic receptor subtypes for learning and memory. There is evidence supporting an action of serotonin to inhibit attentional processes, perhaps primarily through inhibition of dopaminergic function, but also via other neurotransmitter systems critical to attentional function such as the noradrenergic and cholinergic systems. Studies indicate that the serotonin selective reuptake inhibitors may impair aspects of attention, whilst acute tryptophan depletion to reduce serotonin synthesis and release, may enhance aspects of attention. These data have resulted in several researchers proposing general theories of serotonergic inhibition, particularly in respect to attention/arousal. However, differential effects may be seen from studies of the various serotonergic receptor subtypes, which have so far been targeted, indicating a general theory may not be sufficient to explain the data. The evidence presented in this thesis demonstrates that some of the paradigms used thus far to support general theories of serotonergic inhibition of attention/arousal may be flawed. Specifically, monoamine depletion studies may not be able to separate serotonergic and dopaminergic influences on cognition, whilst studies of selective serotonin reuptake inhibitors and chronic ecstasy use have not controlled well for influences of sleep on cognition. Furthermore, evidence from studies of the serotonin receptor subtypes may indicate effects specific to neuropsychological processes underlying measures of attention/arousal or differential effects on aspects of cognition, which may contradict a general theory of inhibition. In conclusion, general theories of inhibition are still sufficient to account for the majority of data. However, in further academic and clinical research, thorough investigation of cognition will be critical to the development of more detailed theory and the development of effective drug treatments for cognitive disorders. Furthermore, the consideration of confounding factors in research such as the influence of sleep on cognition and the competition between monoamines for transport, is critical to the understanding and interpretation of the scientific literature to date.

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