4
Physiology
THE present chapter will be concerned with the physiological functioning of the
hippocampus and how this function can be understood in terms of the cognitive
mapping theory. In the first section we shall consider the hippocampal
electroencephalogram (EEG): its form, its underlying mechanisms, and its relation to
the behaviour of the animal. In particular, we shall be concerned with theta activity,
that rhythmic pattern in the hippocampal EEG which has captured the attention of
many investigators. The various suggestions concerning its relation to behaviour will
be discussed, and we shall propose a function for theta within the mapping system.
Following this we shall consider in some detail the properties of single neurones in
the hippocampus, primarily as investigated in experiments with freely moving
animals. Our own work in this area will form the bulk of this discussion, which will
attempt to define the elements in the hippocampus which comprise the mapping
system. Finally, we shall propose a physiological model for the functioning of the
cognitive map. Our intention here is not to provide a finely detailed, finished model
of the mapping mechanism; we do not have sufficient information at present to draw
a ‘wiring diagram’. However, it will be possible, on the basis of available
information, to outline a model which would fulfill the functions of the cognitive
map as we have described them. It remains for future research to fill in the details.
4.1. Origins of the hippocampal EEG
4.1.2. INTRODUCTION
The hippocampal EEG recorded from lower mammals such as the rat, rabbit, or cat
can be classified into three distinct patterns∗ (see Fig. 12):
(1) A slow sinusoidal rhythm which normally ranges from 3 to 7 Hz in rabbit,
dog, and cat, and 6 to 10 Hz in the rat and gerbil. This rhythm has been called
theta, or rhythmical slow activity (RSA, Vanderwolf 1969).
(2) Large-amplitude slow waves in which the dominant frequency is slower than
in theta and which, with