The way a question is formulated
A brain, like any physical system, dissipates energy and moves towards equilibrium. Nevertheless, there is a difference between a contracted spring and a panther preparing to jump. A brain creates motivation and impels the organism to reach those environmental fluctuations (reward), which may prevent dissipation of its energy. For example, after exhausting inner resources of energy, hunger compels an organism to search for food, consume foodstuff and receive the possibility to replenish its energy stores. Motivation is the most ambivalent attribute of the neuroscience. A motivational concept is applied to both the brain and behavior as a correspondence of objective and subjective aspects of motivation. Motivations are not necessarily a subjective event. Being a subjective mood state, it is induced by a physiological cause and it modulates the readiness to obtain a reward. For the outside observer, a motivation is a phenomenon consisting of the modulation of sensorimotor relations that leads to the generation of actions in response to a previously ineffective stimulus until a certain optimal state of the organism is attained. This definition is similar to that of R.A. Wise [1344], who considers motivation in terms of matter. This aids scientific description of a motivation, but misses the most enigmatic property of motivation, for it is a subjective sense, too. We never resolve the problem of motivation if we consider only one side of the conundrum. Instead, one needs to reveal the physiological processes engendering this sense. One may say that generation of an action depends on an animal’s attitude to the anticipated result. Therefore, we understand a motivation as an organism’s subjective attitude to its current or future physiological state, which somehow modulates generation of actions until an optimal state is attained. How does this subjective attitude arise and how does it modulate generation of action? Motivation itself is modulated by an internal state of a subject, dependent on experience and on the incentive/hedonic value of its reward [195, 196].
If action is predetermined by the environment and by the state of the brain, goal-directed behavior can be treated as an ordinary reflex, i.e. as a reaction to stimuli (inner or outer), based on memory and heredity. This predetermination would preclude motivation as an exclusive object of physiological description. On the contrary, reality of a motivation is equivalent to the existence of free will, whose existence is frequently discussed and which is regarded as a valid object of philosophical inquiry and psychological analysis [1328], but has not yet been addressed in depth by neurobiologists. The problem remaining to be solved in regard to motivation is how behavior can be both unpredictable and goal-directed.
The free will problem does not have a purely academic interest. For instance, we are of firm belief that computer does not possess motivation and free will, since we know in fine detail the whole sequence of calculations that lead to the solution of a task. However, only comprehension of motivation will allow the creation of an artificial object, behaving as a living creature. It is impossible to develop artificial brain on the basis of conventional computers. Usually the choice of actions directed towards the satisfaction of an artificial motivation, is embedded by theorists in the construction of the system or is determined by memory. Therefore, "voluntary" actions are, factually, predetermined. An external programmer must constantly update the system about the proper strategies needed to overcome newly-encountered perturbations. However, it is unrealistic to predict all possible perturbations and disturbances in an environmental state. Hence, it is unrealistic to hope to develop reliable software for a robot control system. Investigation of motivation should help to design self-contained control systems which can function in an intricate environment, have their own goal and therefore be independent. Meanwhile, living systems demonstrate motivational behavior without any visible participation of a programmer. The ‘ideal’ software, which is embedded into brain construction, does not regiment behavior in detail. When the organism attains its goal it is in an optimal state, and no further actions are generated. A deviation from the optimum will result in a change of activity that leads to a return to the optimum. We argue in topic 4 that assuming the existence of non-predetermined actions is a valid theme in neurobiology. It is internally consistent and does not contradict experimental data and rigorous logic. Here we will consider the essence of motivation.
Motivation as a homeostatic recovery
Animals are capable of overcoming obstacles in order to attain a goal and may work hard to obtain food, water, sexual satisfaction, etc. Any motivation produces behavior directed to satisfaction of the motivation, if we discard those unreal wishes and dreams which may never be satisfied because of insurmountable obstacles, but, fortunately, this does not threaten existence. Motivation is satisfied by reward or by avoiding punishment. Any motivation includes an appetitive stage, a goal-directed search for reinforcement and a consummatory stage, the receipt of reward. At the cellular level, motivation reveals itself, as excitation of many brain neurons. For a detailed discussion of motivations, see reviews [201, 206, 297, 370, 656, 689, 799, 887, 892, 996, 1191, 1354, 1115].
The primary goal of living creatures is maintenance of their general physical integrity. An organism is a complex system. It is described by a majority of variables and it generates numerous motivations in order to correct existing deviations from various optima. Sometimes the subject is embarrassed to determine its innermost goal. A. and B. Strugatsky, in their fantastic novel "Stalker", described a unique, but almost inaccessible place. Anyone reaching this place will attain his/her main innermost desire. In the Strugatsky novel, certain youthful poet dreamed of creating a great poem. He overcame a variety of obstacles and endured awful dangers. In the end he has reached this unique place and got rich, but did not write his great poem.
First of all, let us simplify the problem and consider a one-dimensional case in which an elemental motivation depends on an imbalance of only one factor in an inner environment, which evokes the state that is somehow expressed as favorable or harmful for the subject. There are a limited number of such elemental biological motivations: feeding, drinking, respiration, temperature regulation, sexual motivation, avoidance of danger, the need to sleep, and artificial motivations (self-stimulation and drug-dependence). Motivation is undoubtedly associated with the need for stability of the internal milieu or homeostasis [203]. Standard functioning of the organism, a simple continuation of its being, is connected with expenses of energy and substances and is the origin of current requirements that must be satisfied for prolongation of life.
As we already know, homeostasis maintains stability of physiological systems and holds the parameters of an organism’s internal milieu (or correspondence between these parameters) within limits that allow for survival. Yet deviation from the homeostatic equilibrium is not the sole cause for motivation and we will consider as an exception from this rule the examples of sexual and defensive motivations. The starting point of sexual motivation is not determined by metabolic needs and the starting point for defensive motivation lies in the outer environment. Nevertheless, independently from the starting point, the basis of sexual motivation, and may be as the basis of any simple and complex motivation (how to verify?), lies a deviation from the physiological equilibrium. Therefore, phenomenon of motivation is related to the phenomenon of homeostasis. Sometimes, motivation does not reach the threshold of awareness, for instance, the motivation to breathe. In such cases, we may describe the event without attracting the term ‘motivation’ and use as a background only the term ‘homeostasis’. Aware motivation may be included in the term of homeostasis, if we accept that homeostasis can become aware. Previous considerations have shown that, at least in some circumstances, homeostatic disturbances may be connected with completing of high neural functions. We soon will return to this problem and demonstrate the tight relationship between the concepts of homeostasis and motivation.
Apparently, homeostatic motivation might actually reflect a variety of physiological settling points rather than one true set-point, arising as a balance among opposing systems [114]. Besides, there are convoluted motivations that depend on a combination of variables and which defy experimental analysis. Nevertheless, even in these cases, set-points for the homeostatic mechanism may exist according to a theory of a common currency for different motivations [197]. According to this theory, any motivation is directed to receiving a pleasure. There must be, then, a general set-point for homeostatic regulation, when a change in this particular set-point cannot be compensated. We argue that in such cases homeostasis seems to regulate some critical quality of existence, as, for example, the level of damage.
External influences, which are not coupled with the internal state, can affect behavior that does not directly promote homeostasis. Motivation can be associated with learning and memory and plays a leading role in the adaptation of animals to a changing environment. The animal that has already experienced satisfying its demands performs similar actions and satisfies the demand again in the presence of a new motivation. Moreover, a necessity to solve the task can turn into the demand and thus motivation may be complicated [148]. Motivations depending on memory may be extraordinarily specific, allowing us to get information on the essence of motivation from an analysis of the mechanisms of learning, especially instrumental learning. Nevertheless, dependence on memory does not necessarily capture the essence of motivation, for animals can demonstrate goal-directed behavior in early life, without any personal experience. Therefore, it is not necessary to touch ‘memory’ for description of simplified motivation. During instrumental learning, the motivation is created, affects behavior and is satisfied.
Thus, an organism generates action to support the stability of its inner milieu. If the organism has information that this particular combination of the inner constants is optimal, must be maintained, but is disturbed because of intervention of the environment or because of exhaustion of inner resources, its actions will direct it to search for the possibility to satisfy its needs. Whether homeostasis of an organism is entirely based on homeostasis of its cells is unknown, but at the least, cellular homeostasis exists and can affect behavior.
