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INTRODUCTION +1190Despite the large number of studies on all aspects of the hippocampus, the function of this structure is still an enigma. In our view multidisciplinary studies of input-output relations integrated with behavioral analytical inves tigations hold the greatest promise for a solution to this problem. Therefore, this review is dedicated to the basic physiology of the hippocampus seen as a group of input-output subsystems.The first several sections deal with the functional anatomy and electro physiology. This subject receives more intensive treatment in those sections where recent anatomical data obtained with tracer techniques have pro vided signifi cant advances. In the second half of the review, hippocampal behavior correlates are dealt with. The insight of the authors into these aspects is here given precedence over a detailed review of the extensive literature. The treatment of transmitters and pharmacological aspects is omitted here in view of the recent comprehensive review of . Several reviews of the physiology of the hippocampus have been published. A classic is that of Brodal (39). The last physiological review is that of Green (86). Since then there have appeare d reviews on the phar macology of the electrical activity of the hippocampus (196); on the physi ology of cellular processes (189); and on behavioral correlates of hippocam pal function (4, 63, 1l3, 141). The comprehensive book of Isaacson (103) gives a survey of the limbic system. A collection of papers on several aspects of hippocampal structure and physiology, its relation to behavior, its devel opment and neuroendocrinology has been edited recently by Isaacson & Pribram (104). A book covering the Russian literature on the hippocampus has also appeared (76). 185 0066-4278/78/0301-0185$0 1.00 Annu. Rev. Physiol. 1978.40:185-216. Downloaded from www.annualreviews.org Access provided by University of British Columbia on 11/25/14. For personal use only.

In previous studies (Lopes da Silva and Kamp 1969;Kamp et al. 1971;Arnolds et al. 1979), we have shown that there is a significant rhythmicity in the theta band of the dog's hippocampal EEG in the majority of behavioural states investigated (e.g. lying down, standing, eating, walking) and that transitions in motor behawour are correlated with shifts m amphtude, frequency and rhythmmity of the theta component m the hlppocampal EEG. These results m combination with data from the literature concerning rats, rabbits and cats Kemp and Kaada 1975) suggest that the spectral propertms of the dog's hlppocampal EEG reflect motor activity and sensory inputs in a non-specific but predmtable way, as was argued in our previous work Arnolds et al. 1979). In order to substantiate this notion further we designed an experiment to determine whether the mtenslty of motor behavmur is reflected m the hippocampal EEG (part I of this study).The motor behavioural correlates of the hlppocampal EEG are described in many cases m the hterature at the level of goal-d~rected behaviour (walkmg towards or away from a goal) or m the context of particular mot1- This led us to mvestlgate whether such elementary motor acts would also be correlated with the properties of the hippocampal EEG. Thus m parts II and III of this study we describe the hippocampal EEG correlate~of steps, sighs, and of a motor reflex. This paper is based on an mtensive longitudinal study of 2 dogs. This approach allows a precise comparison of the EEG and behavlOUt recorded in different but exactly reproducible situations m the same animal. A prehminary report on these mvestlgatlons has been pubhshed elsewhere . In both dogs the electrodes were placed in the caudal 'knee' of the hlppocampus near the CAl-subiculum border. The positions from which we recorded are indicated m Fig. 1 by round black dots. In Fig. 1B the squares indmate the positions of some other electrode tips in the same bundle. The uppermost yielded large amphtude theta rhythm with important high frequency components. The tip located m the pyramidal cell layer yielded a rather irregular EEG of smaller amplitude while the electrodes below the pyramidal cells all gave a highly isomorphm clear rhythmm slow activity (RSA). Hence one of these was used for analysis.

Key words: hippocampus EEG -motor behaviour -vestibular inputs -eye movements -rhythmic slow activity (theta rhythm) -catIn cat the relation between various behaviours and the spectral properties of the hippocampal EEG was investigated. Both EEG and behaviour were quantified and results were evaluated statistically. Significant relationships were found between the properties of the hippocampal EEG and motor acts (walking, sitting, eating, stepping and eye movements). These results were compared with those obtained in dog under similar experimental circumstances. Species differences were found particularly regarding the fact that in the cat a dissociation between frequency and amplitude parameters was obtained for some behaviours; this may explain why appreciable differences in the visual interpretation of EEG records of different species are often reported. A simple model of the modulation of hippocampal EEG by brainstem inputs is presented. Particular attention is paid to species differences regarding the anatomy and physiology of the pathways involved in this modulation. It is concluded that in cat a strong relation exists between the modulation of spectral properties of hippocampal EEG and vestibular inputs and/or eye movements. The effects of body acceleration on hippocampal EEG are put in evidence and related to theories of hippocampal function.