Electrophysiological perspectives on locus coeruleus: Its role in cognitive versus vegetative functions

Abstract

The hypothesis that the locus coeruleus (LC) may be involved in the control of cognitive and/or vegetative processes is reviewed, primarily focusing on electrophysiological experiments. With the impact of this nucleus on target neurons in different brain areas and with the activity pattern of LC neurons in conscious animals, the electrophysiological data are, to a large extent, in keeping with the postulated role of the LC in cognitive processes. A considerable body of evidence from lesion and stimulation experiments points to a possible function of the LC in the control of autonomic processes. In particular, many studies suggest a role in the central control of blood pressure. The electrophysiological data, although not entirely ruling out such a function, are not in keeping with this hypothesis. In conclusion, although there is a case for the LC's having a role both in the cognitive sphere and in the vegetative sphere, the exact role of the LC in both of them remains to be elucidated.The locus coeruleus (LC) is a brain nucleus which persistently attracts numerous scientists to use a variety of methodological approaches and methods to study its functions. Over the past couple of years, these studies have provided a steadily increasing list of postulated roles for the LC. Unfortunately, this list is not only long but also contains numerous inconsistencies. The primary postulated functions of the LC, most of which have been proposed on the basis of behavioral investigations, are summarized in Figure 1. The suggested functions can be divided arbitrarily into those related to the cognitive sphere and those belonging more to the vegetative or emotional sphere. The role of the LC in the control of attention (Pisa & Fibiger, 1983) and processes related to learning and memory (Hagan, Alpert, Morris, & Iversen, 1983;Mair & McEntee, 1983) is still debated. The amine hypothesis of mood control has still not been proven but remains, at the moment, one of the most attractive hypotheses concerning the etiology of depression. Although a considerable body of clinical and animal experimental data speaks in its favor, it may ultimately turn out to be incorrect.It is not possible to cover in a single article all the postulated functions of the LC. Therefore, we chose to discuss in a synoptic manner only two aspects of the LC-(1) the postulated role in cognitive processes, and (2) functions in the vegetative sphere. Both will be discussed primarily from an electrophysiological point of view. The first topic we selected because most electrophysiological data are in keeping with this hypothesis. The second topic was included because, interestingly enough, it strongly challenges the role of the LC in cog-The authors' mailing address is: Biology Research Laboratories, Pharmaceuticals Division, Ciba-Geigy Ltd., 4002 Basel, Switzerland. nition. The list of putative functions depicted in Figure 1 is incomplete, and some of those not mentioned will be dealt with in separate papers of this issue. Traditionally, the LC has mostly been cons...

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