Monitors: Key mechanisms and roles in the development and aging of the consciousness and self

Abstract

A network of interacting neural structures, called monitors, exists in the mammalian brain in which data derived from sensory inputs and from memory stores is precisely displayed within the brain. The key function of monitors is to provide an ‘ultimate monitor’, proposed to be the locus that generates the phenomenon of conscious self awareness, with information that defines or maps the positions of the parts of an individual with respect to each other and with respect to external objects or events at specific times. The resolution of at least some of these monitors (e.g. some concerned with vision) is extremely great and approaches, in the case of vision, the precision with which images of external objects are projected onto the retina. This conclusion is based on the fact that an individual is able to perceive visual images with an acuity that closely approximates the fineness of resolution of the retinal image. The sensory signals that provide information about body part positions and those that provide information about the exterior are evidently integrated with each other in a suitable hierarchy of monitors so as to provide a coherent representation of self- vs.-environment. The logical ‘framework’ monitor for this integrated dislay-mapping is proposed to be that the maps the body in space and it is proposed that the locations of objects perceived through the touch sense and senses that deal with more remote items in the environment become superimposed on a map that extends or extrapolates the body space map beyond the body's physical boundaries, a learning process that occurs during development. The ultimate monitor not only receives a display of the synthetic representations derived currently through the integrative functions defined above, but also is provided with at least four other inputs from other different classes of monitors. One of these is a monitoring system that generates timing signals needed to separate inputs into a time order and to assign an order to them. It is proposed that it is awareness of these timing signals by the ultimate monitor that is the essential and indispensible input that generates the phenomenon of awareness. A second input to the monitor that is the self is a selected part of its own activities. This awareness of what the ultimate monitor is receiving, doing or planning to do in the future is the characteristic necessary for awareness of self. A third monitored component input is information that is selectively retrieved from memory, including memories that define the past actions and states of the self monitor. The representations presented to the ultimate monitor from memory are generally much less precisely defined than those provided by current sensations. This implies that what is stored in memory as records of past sensations represents partially abstracted and simplified imagery or sequences that reflect the essence of sensory experiences denuded of fine details. The fourth kind of display transmitted to the ultimate monitor is one that represents the affective feelings associated either with current input or recalled out of associative memory. This last kind of experience or relived experience (recalled memory) is central to the use of the other information provided to the ultimate monitor in fulfilling its key role -- the making of decisions regarding which of possible alternative actions (usually movements) is most appropriate to a perceived relationship between an individual and objects in its environment. Alternative mechanisms through which representations possessing the observed precision may be generated in a mature vertebrate brain are discussed and it is concluded that a general or ‘coarse grain’ projection of patterns in the source a monitor displays is determined genetically-developmentally but that the ‘fine grain’ resolution that an adult enjoys is the result of learning during development. This learning, it is proposed, results from the fact that points nearby to each other in space or time in a source are more likely to be concurrently active, which fact causes a fine structure remapping of the monitors. The means through which symbolically coded representations of experiences are retrieved from memory and reassembled in a suitable monitor for projection to the ultimate monitor are assessed and possible means for attaining this structural retrieval are proposed. Finally, alternative mechanisms for the generation of timing-clocking signals are discussed, the precision of such timing is evaluated and two of these mechanisms are indicated as possible means. This paper provides the conceptual framework for an analysis of neuroanatomical structures and their relationships to each other upon which the tentative assignment of particular functions to particular brain structures is based, as described in a companion paper (Strehler, B., Mech. Ageing Dev. (1989) submitted).