Fabio Ruini’s blog

The behaviour of organisms has both a strategic level and a tactical level. The strategic level is the level at which an organism decides the particular activity that the organism has to execute at any given time. The tactical level is the level at which the organism executes the specific behaviours which constitute the activity decided at the strategic level and which make it possible to reach the goal of the activity. The tactical level is obviously important because it is the actual level of behaviour. But the strategic level is even more critical because to survive and reproduce all organisms have to accomplish many different activities and they generally cannot be involved in more than one single activity at any given time. Therefore, there must exist some mechanism in the organism for deciding to which specific activity to dedicate itself at any particular time. Examples of different activities are eating, drinking, avoiding predators and other dangers, finding a partner for reproduction, insuring the survival of one’s offspring, sleeping, reacting appropriately to physical pain. At one given time the organism must decide, for example, to eat, and not to drink or to find a partner for reproduction or to sleep, and then it must execute the specific behaviours in response to environmental stimuli that allow the organism to eat. The two levels of behaviour may be labelled “motivational” (strategic level) and “cognitive” (tactical level). An organism’s chances to survive and reproduce depend on both its capacity to manage appropriately the competition between different motivations and to choose the specific motivation that must govern its behaviour at any given time and its ability to generate the appropriate sensory-motor mappings that constitute the activity aimed at satisfying its current motivation.

In this chapter we will illustrate the distinction between the strategic and the tactical levels of behaviour by describing a series of simple computer simulations in which a population of organisms evolves in various types of environments.

Very often the strategic level involves the arrival of information from the organism’s body to the organism’s brain. For example, if the organism must decide whether to look for food or to look for water the organism’s body must inform the organism’s brain concerning the quantity of energy (hunger) and of liquids (thirst) currently contained in the body. This input from the body arrives to a motivational circuit that acts together with the sensory input from the external environment to determine the organism’s behaviour. More specifically, the input from the body (motivational input) may have an attentional role in the sense that it allows the organism to respond to some part of the current input from the external environment and to ignore the remaining part. For example, if an organism is hungry but not thirsty (the organism’s body informs the organism’s brain that there is little energy but sufficient liquids in the body), the organism will ignore sensory input from water and respond to sensory input from food by approaching and eating the food.

However, since the body constitutes an internal environment that co-evolves with the brain in order to insure the organisms’ reproductive chances, it is possible to show that a system for informing the brain about the current level of energy and liquids present in the body is more useful in certain environments with a given distribution of food and water than in other environments with a different distribution of food and water. In other words both the motivational and cognitive capacities of organisms evolve in function of the particular environment in which the population of organisms happens to live. The different environments and the different motivational systems are also reflected in the behaviour exhibited by the organisms in a controlled (experimental) situation in which an individual is exposed to both food and water and it has to decide whether to approach food or water.
For other motivations, however, it is the sensory input from the external environment which triggers the motivational choice and causes the organism to decide the activity to execute. In an environment that contains both food and predators an organism can look for food when the predator is absent but must cease looking for food and react appropriately to the predator (for example, by flying away from the predator) when the predator appears. These simulations indicate that it may be important for an organism’s brain to include a special motivational circuit which is activated by sensory input from the external environment and acts together with the cognitive circuit that maps sensory input into motor output. This motivational circuit may reside in different parts of the brain with respect to the cognitive circuit (e.g., sub-cortical vs. cortical), may have different structural and functional properties (more rapid and more prolonged action), and may result in more effective (adaptive) behaviour.