Personality is a complex dimension that describes the behavioral, cognitive, and emotional pattern of an individual; by which he expresses himself as an independent being within the human multiplicity.

Scientific interest in knowing what personality is and how it manifests itself has led many researchers, over the years, to postulate different theoretical models for this purpose. One of them was Jeffrey Gray, who presented his theory of sensitivity to reinforcement as an alternative to classical models (that of Eysenck, for example), but starting from a fundamentally neuropsychological basis.

In this article we will deal with the author’s theoretical postulates, which constitute a very important vision of the nature of acts and cognitions, from which we will be able to better understand who we are and why.

Theory of sensitivity to reinforcement

The theory of sensitivity to reinforcement tries to explain what a human being is like based on his motivation to approach or move away from environmental stimuli or situations at his disposal .

While it is true that there are a number of appetite stimuli to which an innate quest has unfolded that have not been mediated by learning (such as foods to nourish us), others have acquired their positive nuances through individual experience.

The theory contemplates both types of stimuli : those that provoke an unconditional approach or rejection (learning shared by the whole species throughout evolution) and those that generate similar responses but as a result of personal experiences (avoiding dogs because we had an unpleasant encounter with one of them or because we saw a third party being the victim of an attack, for example).

The desire of approach and of rejection/run away (maintained by states of motivational type), would depend on the activation/inhibition of a series of neural networks, which would rise as the organic substratum of the basic dimensions of the personality. According to this perspective, what we think, feel or do can be captured through a reduced group of attributes that sink their roots in the brain (offering a parsimonious and clear explanation of behavior from their multiple interactions).

After a thorough study of the neural structures, and equipped with a broad theoretical background on their functions, Gray proposed three brain systems that would be at the base of the approach and departure behaviours : the behavioural approach system (SAC), the behavioural inhibition system (SIC) and the fight or flight system (SLH). Each person would present a specific pattern of activity for each of them, which would shape the profile of how they act and feel in their natural environment.

Based on these observations, he further proposed two dimensions of personality: anxiety and impulsiveness, different from those usually considered. Each of them would be linked to one of the systems outlined and would also involve different emotional experiences.

As can be seen, Gray drew a direct relationship between brain and personality , understanding that both behaviour and thought could be explained from the activity of the structures involved in their systems. In the following we will connect these two phenomena, explaining in a simple way how neurology and psychology converge in this interesting integrated theoretical model.

1. The behavioural approach system (SAC)

The SAC is a neurological mechanism that favors a behavior of approach towards the stimuli that have been conditioned in a positive way (that is, that are associated to desirable results or that allow to avoid adverse consequences), motivating with it the active search of its spatial and temporal proximity. Thus, it would be responsible for promoting the availability of what is perceived as desirable or that increases the probability of survival.

All this would translate into a voluntary motor and emotional approach behaviour , mediated by coordinated brain structures. Specifically, dopaminergic fibers that emerge from the midbrain (ventral tegmental area and nucleus accumbens) towards limbic regions such as the basal ganglia, as well as others of a neocortical type (sensory-motor, motor and prefrontal cortex). The activation of this system would manifest itself in positive effects associated with the impulsivity dimension.

The basal ganglia are responsible for the planning and integration of the voluntary movement, as well as for motivation and emotion, while the motor and sensorimotor areas are necessary to translate everything into explicit actions of approximation .

This is complemented by the function of the frontal lobe (which includes intention and projection at an executive level) and the reward system (which brings a positive tone to the life experience through the production of dopamine).

2. The behavioural inhibition system (SIC)

The SIC is understood, in the context of the theory of sensitivity to reinforcement, as a response that is opposed to that of the SAC. In this case it would be activated in the face of stimuli that have been conditioned in a negative way (since they generate a damage or prevent the achievement of something desirable), or that have been fixed throughout the development of the species as objects or situations to be avoided. This is why they promote behaviors that aim at an active distancing.

It also extends to new or overly ambiguous situations, where it is necessary to act in a considered manner and pay special attention to the environment. Consequently, the action of approaching would be inhibited until more precise knowledge was available about the nature of the facts being faced, from which moment a series of behaviours of proximity (mediated by the SAC) or of avoidance (mediated by the SIC and the SLH) would be articulated.

The brain structures that form the SIC are the hippocampus and its projections towards the prefrontal cortex . The hippocampus would actively participate in memory and spatial orientation, while the prefrontal cortex would be responsible for attention and prospective reasoning. All of these would be coordinated to explore the immediate environment and predict what may happen at that moment or as a consequence of it at a later time.

The system, therefore, is directly associated with anxiety and is in charge of continuously assessing (monitoring) the situation in which we are immersed and what could happen in the future, with the aim of anticipating the appearance of adverse events that we fear or that we consider should be avoided.

3. The fight or flight system (SLH)

The SLH is related to the escape from adverse events in which one is involved (which differentiates it from avoidance) and to fight or flight behaviour.

The brain structures involved are the amygdala (in which various emotional experiences are processed, but particularly fear) and the hypothalamus (which mediates stress responses and activation of the autonomic nervous system). Anger and fear would depend on it, emotions that have the purpose of preparing the body to give an immediate response.

It is known that the simultaneous hyperactivation of this system and the SAC triggers an approach and escape behaviour at the same time and towards the same object, a setback that would have to be solved by the participation of the SIC. This dissonance between the appetitive and the aversive would be responsible for anxiety as a symptom within a disorder.

How would one understand personality from this model?

To explain personality according to the theory of reinforcement sensitivity, the SAC and SIC systems are considered in particular. Both work independently, so that the high or low activation of one of them would not influence the other. Thus, there would be people with hyper/hyperactivation of both systems, and others in whom one would be hyper-activated and the other hypo-activated .

As previously stated, the SAC would be related to impulsivity and the SIC would be related to anxiety, these being the basic dimensions of the personality according to Gray’s model (thoughts or acts of approximation and inhibition respectively). In this sense, subjects with hyperactive SAC would be impulsive, and those with hyperactive SIC would be anxious.

Some authors have drawn analogies to explain that the spectrum of activation of the SAC would be associated with continuous extraversion/introversion (tendency to sociability or preference for solitude or individuality) while the SIC would do the same with neuroticism/stability (vulnerability to emotional distress or regularity in affective states).

At present, the theory of sensitivity to reinforcement is the subject of numerous investigations , from which both favourable and contrary results have emerged. Some of them suggest that the SAC and SIC systems could be related in some way (so they would not work independently) and the study of anxiety/depression is also being approached from this same prism. Time is still needed, however, to understand the real scope of Gray’s model.

Bibliographic references:

  • Bijttebier, P., Beck, I., Claes, L. and Vandereycken, W. (2009). Gray’s Reinforcement Sensitivity Theory as a framework for research on personality-psychopathology associations. Clinical Psychology Review, 29(5), 421-430.
  • Colder, C.R., Trucco, E.M., López, H.I., Hawk, L.W., Read, J.P., Lengua, L.J. … Eiden, R.D. (2011). Revised Reinforcement Sensitivity Theory and Laboratory Assessment of BIS and BAS in Children. Journal of Research on Personality, 45(2), 198-207.