Laterality and crossed laterality: what are they?

The body of the human being, like that of almost all the bodies that populate the set of forms of animal life, follows some symmetry patterns.

We have two arms, two legs, two eyes and a nose on our central axis, and the same logic is repeated in the arrangement of almost all of our organs. We are adapted to perceive and act in much the same way both to the left and to the right.

What are laterality and crossed laterality?

As you might expect, these same rules are embodied in the shape of our brain. We have two cerebral hemispheres, each one on the left and right, which are something like mirror images of each other... at least with the naked eye. In reality, both hemispheres are very different at the cellular level and, in fact, are responsible for different processes. We all know that idea that says that the right hemisphere is rational and analynic, while the right 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, since each of these halves

is related to one of the two hemispheres of the brain. For example, almost everyone has a dominant hand and we consider ourselves right-handed, since we use the right 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 for the opposite to happen with their eyes or legs. These are the cases of crossed laterality.

Cross laterality, homogeneous laterality and dominance

Normally we speak of homogeneous laterality, because people whose dominant hand is the one on one side tend to have the dominance 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 these dominances will be what defines whether there is a cross or homogeneous laterality.

In any case, crossed laterality is one more form of laterality, and the existence of one type or another is a consequence of the functioning of our nervous system. That means that it is in the interconnections of our different parts of the body from the nerves where they have to Look for the causes of one or another type of laterality, and this can also be defined by the areas of the body to which it affects. In that sense, there are different dominance classes that serve as criteria to define the type of laterality:

1. Manual dominance: defined by the dominance of one or the other hand when picking up objects, writing, touching, etc.
2. Foot dominance: defined by the dominance of one or the other foot to kick, kick a ball, stand on one leg, etc.
3. Auditory dominance: tendency to use one ear or the other more to listen, put on a headset, etc.
4. Ocular or visual dominance: defined by the dominant eye when looking at it.

Why is there cross laterality?

The nervous mechanisms by which one or another type of laterality occurs are not well understood, nor why sometimes there are cases of crossed laterality, since the majority is that there is a homogeneous one. In any case, the crossed laterality would be proof that there is no great center of planning in charge of coordinating the different dominances or that, if it exists, its function or is essential.

In any case, it is currently believed that cross laterality could cause some problems when it comes to coordinate the parts of the body whose dominance is discordant, such as when it comes to to write. Research is lacking in this regard, but it is considered cautious take into account cross-laterality as a risk factor in the appearance of learning disorders in children.

In any case, as the system of connections between neurons on which dominance is based is highly plastic (it is that is, adaptable according to our learning and experiences) laterality is not determined only by genetics, but also also it is influenced by the learned behavior, culture, habits, etc.

Cross laterality is no exception to this rule, and therefore it can be learned to mitigate the effects of a very extreme dominance to also use the homologous part of the body in the other half, going on to speak in this case from forced laterality.