The Memory of the Senses

Author: Noelia Rico Berbel (Student of Nutrition in UMH)


Ranulfo Romo Trujillo (Ures, Sonora, Mexico, August 28, 1954) – is a Medical Doctor, researcher and professor specialized in Neurophysiology. He has written over 100 scientific articles and published 6 books, including:

  • Presynaptic inhibition and neural control (1998), in collaboration with Pablo Rudomin and Lorne M. Mendell.
  • Acople cerebro-computadoras: ¿matrimonio en ciernes? (2008), in collaboration with Pablo Rudomin.


Despite its apparent stillness, the world is in constant movement. The Sun, Earth, Galaxy and Universe are in constant dynamics. The senses are in charge of informing of these changes, although are confusing at times. In this manner, although there are moments where no change is apparent, everything is in constant activity. The cells of an organism or our ideas in constant renovation due to our brain´s activity are clear examples. The environment´s changes are mainly perceived by the senses, such as our eyes, in the form of electric signals. However, this key role that the senses play are partly due to one´s “memory.” This will be the focus of this chapter, where Science and Philosophy intertwine.

The first aspect to point out is that the present does not exist. This seems to be a very decisive affirmation, but can be observed in a very simple example: Alzheimer´s patients, with their brain circuits of past memories lost, are capable of feeling, seeing, hearing, and tasting, but cannot recognize a family member or answer a question. This demonstrates that the absence of brain circuits with past memories it is not possible to know who we are now. In fact, all this occurs in the past, the present is the past, due to the time that it takes to process a stimulus or organize a movement.

This observation forces us to question what the brain does when memory is lost. Thanks to the brain´s properties, it is capable of surpassing what has been learned and generalize. It can transform experiences without discerning what is real and what is acquired by the senses, or including what was an illusion. The interesting works published by the neuroscientist Ranulfo Romo with Rhesus monkeys demonstrated that at higher stimulus, less neuronal response is produced. This challenges the current idea of the relation between stimulus and neuronal response. The studies demonstrate that it is not possible to focus on a stimulus indefinitely, rather the attention decreases with time until the individual is not capable of focusing on the stimulus even if it is present. This theory is applicable to many daily aspects, such as the inability to always eat the same food or look at the same place. However, sometimes there is a perception that nothing changes and memory is lost.

In order to create a sensory-based memory, the stimulus is sent to the cerebral cortex by the receptors that receive the stimulus. In this manner, flavours are captured by the taste buds of the tongue. The olfactory receptors also react with this stimulus. The highly-sensitive lips help locate the food of babies. However, the most important “receptor” are the hands, which are vital for human survival, as well as to recognize the environment, send feelings and receive stimuli.

All the sensorial receptors connect with the cerebral cortex in a certain area. The most important stimulus are given a larger brain area, with the fingertips presenting the highest number of nerve endings. These areas dedicated to sensorial receptors vary among the individuals, and can change throughout the lifespan of an individual depending on their activity. In this manner, a bread baker loses sensitivity to heat, and a pianist or guitarist have more sensitive fingertips when playing a musical instrument.

However, despite the importance of touch, the most stimulated sense is sight, and is considered to be the most credible sense: “seeing is believing.” Regarding sight, that are those that believe that the colours do not exist but are rather a product of the brain. In reality, all physical perceptions are products of the brain. The reality that is created in a human brain does not necessarily have to be the same as that created in other animal´s brains. In this respect, colours are not an exception to how an important part of memory is created.

In this manner, throughout history and in different languages there is the concept of “black and white”, as representations of light and dark. Then come red, followed by green and yellow. However, blue, brown, grey, orange and pink are not paid as much attention, corroborating the theory that different colours are perceived in different degrees. Colours are the product of different light wavelengths, but is really much more. The eyes receive the light rays, where two types of cells are present. The rods absorb light with almost no variation, only differentiating if there is light or not, and generally activate when there is little light. The cones, on the other hand, classify light in various levels of red, green or blue. The most sensitive receptors react to blue light, which perceive it as black when they are saturated.

Besides distinguishing different wavelengths, the eye can detect the number of photons it is receiving, interpreting this as brightness. The most sensitive wavelength regarding brightness is with the colour yellow. Grey is the sum of all wavelengths but at low intensity, such as a dim white light. The brain constructs various brown colours when the eye perceives low-intensity yellows or oranges. Also, the colour rays when mixed with white light make new colours, such as pink, which is red with a low level of saturation. In other words, the combination potential is infinite as the retina acts as a mixing palette: “We create colour.”

What about smells and taste? For a long time it has been considered that certain memories derive from tastes perceived in infancy. The neurologists know that the taste cells have a low renovating capacity, indicating that memory is formed from smells. In a similar manner, the receptor of the nasal mucosa play an important role for colours. These receptors recognize certain chemical compounds that are connected with certain brain areas, generating smell representation maps. The memories from olfaction are stored in the most ancient part of our brain. In this manner, when a smells is perceived in the adult that was previously experienced in infancy, the associated auditory, visual and affective are also activated with the olfaction. Therefore, olfaction is the first sense to develop, the most enriching and essential for survival. It is also present in the limbic system (where the emotions are regulated), intertwining with the fibres that process pleasure.

Ranulfo Romo has spent over 30 years on perception neurology. He affirms that we will never completely understand ourselves, since “the brain is constantly trying to understand itself.” If it is tricking us, we will never know if we truly understand the brain or the brain is allowing us to believe that we understand it. Also, this demonstrates that the world that we know does not exist without memory. To this end, the senses play a fundamental role.