Attention in cat revisited. A critical review of a set of brain explorations in fully alert animals

Abstract

Introduction. The greater majority of animal studies based on the ongoing electrocortical activity have been devoted to correlates of sleep-wakefulness, with their characteristic rhythms with a large cortical distribution. By contrast, “focal” rhythmic activities, with limited cortical extent were surprisingly not so often explored so far in animals. During the past 50 years, we precisely adopted this strategy to analyze attention in cat and shall herein try to summarize and critically examine some of our data obtained over the years. Methods. All experiments were carried out on adult animals implanted with cortical electrodes, and in some cases also with subcortical macroelectrodes stereotaxically introduced to reach the requested levels1. Cats were daily introduced into an experimental space (about 2 m2) which contained both a rectangular perspex box and a vertical opaque wall with a small hole at its base (see Fig. 1). Within the space, the cat would face one of two possible experimental situations, alternatively day after day. In situation 1, a living mouse was left free behind the wall and the cat used to remain quasi-immobile close to it, apparently waiting for a possible appearance of the mouse at the hole. In situation 2, the living mouse was instead placed into the closed perspex box and the cat, again free in the space, used to stay or sit close to the box, watching the mouse. The surprising fact was that in both situations, the cat would generally maintain its particular attitude, almost motionless either waiting or watching, for more than 30 mn. As indicated by the electrooculogram (EOG), the animals made very few eye movements during these attention episodes. More recently, in order to know more about the ECoG during a saccade, we changed our protocol, now placing the animal into a cylindric space where it could observe a moving vertical bar suddenly appearing and then stopping. All brain activities and the EOG were dispatched through a flexible lead to the amplification and processing devices with auto- and cross-correlation analyses and, more recently, through a frequency-time display (wavelet transform). Except for the initial surgery of electrode implantations; our cats were never submitted to any general anesthesia during the experimentation period. Results. In a first set of data we shall describe cortical activities recorded during attentional states. Most of them were obtained during immobile attention, others during the protocol with attentional shifts. Thalamic recordings and brain stem modulations of the attentive states will follow.