Lateralisation in humans and other vertebrates involves the input of sensory information more strongly to the brain hemisphere responsible for a required task. Examples include eye preference, and asymmetric inputs of sound and smell , which improve cognitive tasks when individuals process stimuli. Interestingly, the degree and direction of lateralisation can also vary between individuals depending on personality phenotype, which affects their behavioural responses towards stimuli. However, it is not known how sensory information is lateralised when processing stimuli and simultaneously organising a behavioural response towards them. In a recent study we show that this can be accomplished by separate senses being lateralised differently. We demonstrate for the first time that electrosensing is lateralised in weakly-electric fish, Gnathonemus petersii, and find that the direction of laterality towards an unfamiliar object varies with personality; bold fish lateralise towards the right and timid fish the left hemisphere. By contrast, visual inputs do not vary between individuals, but are lateralised across the population towards the left hemisphere, responsible in fish for the analysis of unfamiliar objects. This species has a stronger representation of electrical than visual signals in its brain , which could drive the differences between senses in functional laterality. This novel observation reveals that different senses can be selected for lateralisation in different ways, depending on their dominance, which has implications for the evolution and development of brain structure.
Individuals act differently under the same conditions; everyone can be either afraid of danger or brave in the face of risk, but to what degree varies. Some individuals are bolder and others more timid, but when they work as a group they benefit from reduced risk, better defense and collective detection of danger and resources. To achieve this individuals co-operate, collaborate and synchronise their actions. One way to do this is to assign ranks and have a hierarchical system, where some individuals lead and others follow. This is part of human and animal communities alike. Take for example military types of organisation and even political ones. An alternative is to opt for a democratic system, that relies on majority decisions (consensus), such as our electoral system. In human society both systems are interchangeable and fused, look at for example the merit-based hierarchy of private companies which coexists with shareholder and directorial consensus policy-voting. In animals, both systems can also arise depending on external conditions. To find food, a knowledgeable animal may lead others, but deciding between alternative food locations consensus will determine where the group will go. Alternatively, inter-group factors may also affect organisation, for instance the spread of directional changes when navigating relies on how close individuals are to perceive and pass the information. Could another internal factor be the degree in which individuals differ in their personality tendencies?
We found that the average personality of zebrafish individuals constituting a group and the degree of variation between them does not majorly affect their collective response. However, we also found that group behaviour at any situation reflected the average of individual behaviour at that same situation. Thus the adjustment of group actions to the average of its members is not generic, based on personality, but specific to current conditions. A consequence of the increased risk-taking in groups is that differences between individual and collective behaviour were greater for more timid individuals which might be a result of the safety-in numbers groups provide.
Like fish, humans are also a social vertebrate and we can possibly see how similar effects are responsible in how we collaborate: each individual compromises until agreement is reached, but the compromise is greater for animals which as individuals act most different than the agreed actions of the group. We found that that reaching this agreement can be difficult for very different individuals. Zebrafish groups composing individuals that varied most in their boldness, took longer to make a collective choice and were more likely to split before they reached consensus. This means that more similar individuals are better at reaching agreement, but it could also mean that groups of more different individuals might be disadvantaged when facing new decisions. Similarly, human populations can vote almost evenly between two choices when the opinion of the population is split between two highly contrasting views (see recent British referendum and American election results), making strong-majority decisions difficult to reach.
We are often determined by our personality, a set of traits that develop during our lifetime and make us who we are. Our personalities can determine our actions and our emotions. Can they, however, determine how we process information? The way we assess our surroundings is intricately linked to how we feel and act. A typical pattern is that an unusual situation might impose fearfulness and stress, which can lead to the negative assessment of that situation and our active avoidance of it. However, an individual with a bolder personality is less likely to avoid and more likely to approach a novel situation, which could indicate a less pessimistic assessment. Recently, personality-based cognitive biases have been tested in animals, but mostly from the perspective of speed-accuracy trade-offs. These trade-offs propose that animals with bolder personalities are likely to make haste decisions; decisions which are faster but less accurate. The evidence is convincing, but attempts to apply it to other processes of cognition, e.g. learning and memorisation, have been less successful. For example, bold guppies are faster at learning from others, but are not less accurate. This is because cognitive processing is complex, consisting of several interacting functions. Therefore effects may be limited to particular functions or affect some functions indirectly through others. Further, personality determines particular tendencies which can be intricately related to how individuals prioritise risk and reward, but also how they collect information and make associations. For one, personality may influence information-collection, via levels of active exploration. In addition, more reward motivated personalities may be able to associate a reward to an act or a stimulus, e.g. food to locations, faster. In this new study on elephantnose fish, we show just that. Bolder fish, which exhibited higher levels of exploration and shorter approach tendencies, also decided faster and were more accurate during training at reaching a food-rewarded location. As an indirect effect of their greater accuracy they also learned faster, which shows that indeed the explorative, reward-driven behaviour of bold fish predicts their cognitive performance in a spatial context. Therefore, by affecting our assessment and our behavioural response to risk and reward, personality also affects our ability to make associations and learn.
Human personality has fascinated us from early on. Aristotle, in his ‘Nicomachean Ethics’ identifies that humans “acquire a particular quality by constantly acting in a particular way… you become just by performing just actions, temperate by performing temperate actions, brave by performing brave actions.”. Today personality in humans and animals is defined in an almost identical fashion, attributed by consistency in behavioral and emotional states. Our modern understanding is a resolution of evolved views corresponding to the parallel development of three fields: psychology, neuroscience and behavioural science. Findings by these fields share the understanding that temperament or personality is partly genetically inherited by next generations, but personality phenotypes develop during lifetime. Therefore, they are variable with conditions, experiences and changes in associated physiology.
The flexibility of personality, albeit more prominently supported in studies on humans, is now also at the forefront of animal behaviour studies. While the definitions applied in animal studies have been generally insistent on the consistency of phenotypes, animals require plasticity or flexibility in order to adapt to changes.
Peters’ elephantnose fish can maintain sensing in light and dark conditions, perceiving shape, distance, size and electric properties of objects. They do this by producing their own weak electric signals which then interact with the environment and are sensed back, like sonar but with electric rather than sound waves. Their chosen environments in the Niger and Congo delta are dim or dark, and one adaptive explanation for this is that they can avoid visually orienting predators. In a recent study on this fascinating species we found that consistency in their level of boldness to approach and explore was only exhibited in the light, whereas in the dark all individuals, even those which were constantly timid in the light, behaved very boldly. As a consequence, the degree of change between light and dark was greater for those being more timid in the light. Conversely, those that were constantly bolder in the light simply maintained their level of boldness in the dark. This shows that bolder fish are at a disadvantage by remaining active in the risky bright conditions where they are conspicuous to predators, whereas timid fish prioritise safety when its risky and the location of resources only when its safe. To balance this disadvantage of bolder personalities, the flexibility of more timid animals is an energetically costly process. The trade-offs between the benefits and costs of each strategy, flexible or stable, can be resolved by the variable levels of flexibility/stability within populations. This process suggests that behavioral flexibility varies within populations and maintains trade-offs in selection.
This study demonstrates that personalities in animals, as in humans, can be flexible. However, individuals may indeed vary in this also, with some having more flexible personalities and others more constant ones. This opens new possibilities in how personality might be examined.