Laterality and cross-lateralism: what are they?
The human body, like that of almost all the bodies that populate the set of animal life forms, follows some symmetry patterns .
We have two arms, two legs, two eyes and a nose in our central axis, and the same logic is repeated in the arrangement of almost all our organs. We are adapted to perceive and act in a very similar way both to the left and to the right.
What are laterality and cross-laterality?
As you would expect, these same rules are embodied in the shape of our brain. We have two brain hemispheres, each to the left and right , which are somewhat like mirror images of each other… at least to the naked eye. In fact, both hemispheres are very different at the cellular level and, in fact, they are responsible for different processes. We all know that idea that the right hemisphere is rational and analinic, while the right one is emotional and responds in a special way to music.
These subtle variations mean that for certain tasks we have one side of our body that responds differently to its opposite side, as each of these halves is related to one of the two hemispheres of the brain . For example, almost all of us have a dominant hand and consider ourselves to be right-handed, since we use our right hand for almost everything. However, this fact does not mean that we have one half of the body that is entirely dominant. Interestingly, it is possible for a person to have a dominant right hand, but the opposite may be true for their eyes or legs. These are the cases of crossed laterality.
Cross-lateralism, homogeneous laterality and dominance
Normally we speak of homogeneous laterality, because people whose dominant hand is on one side tend to have the dominances of the rest of their limbs and senses aligned in that half. Therefore, when we speak of laterality we are referring to the different dominances that exist in a person , and the set of those dominances will be what defines whether a crossed or homogeneous laterality is given.
In any case, crossed laterality is one more form of laterality, and the existence of one or another type is a consequence of the functioning of our nervous system. This means that it is in the interconnections of our different parts of the body from the nerves that the causes of one or another type of laterality must be sought, and this can also be defined by the areas of the body that are affected. In that sense, there are different classes of dominance that serve as criteria to define the type of laterality:
- Manual dominance : defined by the dominance of one or the other hand when picking up objects, writing, touching, etc.
- Foot dominance : defined by the dominance of one or the other foot for kicking, kicking a ball, standing on one leg, etc.
- Auditory dominance : tendency to use one or the other ear more for listening, putting on a headset, etc.
- Ocular or visual dominance : defined by the dominant eye when aiming with the gaze.
Why is there cross-lateralism?
The nervous mechanisms by which one or another type of laterality occurs are not very well known , nor why sometimes cases of crossed laterality occur when the majority of cases are homogeneous. In any case, cross laterality would be proof that there is no large planning centre in charge of coordinating the different dominances or that, if it exists, its function or is essential.
However, it is currently believed that cross-lateralism may cause some problems in coordinating body parts whose dominance is discordant, such as when writing. There is a lack of research in this sense, but it is considered cautious to take into account cross laterality as a risk factor in the appearance of learning disorders in children .
Anyway, as the system of connections between neurons on which dominance is based is highly plastic (i.e. adaptable according to our learning and experience), laterality is not only determined by genetics, but also influenced by learned behaviour , culture, habits, etc.
Cross-lateralism is not an exception to this rule, and therefore one can learn to mitigate the effects of a very extreme dominance in order to use also the counterpart body part in the other half, going on in this case to speak of forced laterality .