The world around us: how the brain plans actions (without needing our awareness)
The brain is an organ capable of coding what is happening around us: monitoring the surrounding environment, planning and making decisions, preparing our body for a specific action. A study by San Raffaele researchers now discovered that bodily actions can be planned even without our awareness – that is, even when a target visual stimulus does not reach our conscious perception.
First author of the research, published on the prestigious Journal of Neuroscience, is Dr. Marco Tettamanti, researcher of the Division of Neuroscience at San Raffaele Hospital, who in this interview tells us about the subject of this work.
WHERE THE IDEA OF THIS RESEARCH IS BORN
“In the “In vivo human molecular and structural neuroimaging” Unit, directed by Prof. Daniela Perani, we have been dealing with language, memory and understanding of the meanings of words and objects for years, and much of our research has shown that there is a close link between sensory perception of the objects around us, the cognitive and linguistic representation of these objects, and the motor coding that our brain carries out to allow us to interact with them”.
For example, reading a word like “hammer”, a manipulable object, activates in our brain the same visuo-motor representations that we activate when we actually manipulate a hammer with our hands.
“At the origin of this work we asked: is it or is it not the link between visual perception, cognitive representation and motor action mediated by our conscience? We addressed the question by evaluating what happens when we process visual-perceptual information of an object in an unconscious way, and in particular if even in such conditions there is an activation of the same visual-motor circuits that have been previously observed in conditions of awareness”.
The researchers used a specific neuroimaging technique, functional magnetic resonance imaging (fMRI) at the San Raffaele’s C.E.R.M.A.C. (Centro Eccellenza Risonanza Magnetica ad Alto Campo), to precisely locate the brain structures that are activated for specific tasks or stimuli.
Previous research had already shown that in the frontal and parietal brain regions there are neurons are activated both when we perform an action on a manipulable object, and when we simply observe it. The novelty of the San Raffaele researchers’ study is the discovery that even when the visual information of the objects is not perceived in a conscious way, the brain responds automatically by activating the same frontal and parietal regions that program our actions towards these objects, and hence the possible movements we could perform on them.
CINEMA-LIKE 3D GLASSES
To ensure that the study participants were not aware of the images presented to them, the researchers used a technique called Continuous Flash Suppression. “We make the volunteers wear 3D glasses like those used in cinemas, and we show them some “masked” images. Such images are composed of a geometric pattern – called “Mondrian mask” in jargon – overlaid onto the photograph of an object, making it more or less visible on the basis of a precise contrast manipulation. The glasses are worn so that the blue lens is placed over the dominant eye of the subject. In this way, beyond a precise contrast threshold, the volunteers detect the geometric pattern, but not the object’s image under the mask. In this experiment we have shown that the visual information of the masked object still reaches our brain, where it is elaborated at the unconscious level”.
An important observation derived from this study is that the activation of the fronto-parietal regions is specific to manipulable objects: “In the study we presented a set of manipulable objects (telephone, hammer…) but also a set of images of non-manipulable objects (home, sofa…), that we cannot hold and on which we cannot perform meaningful manual actions. We have observed that the unconscious activation of the fronto-parietal cortices occurs specifically only when manipulable objects are shown”.
Are these results somehow related to mirror neurons? “Yes, even if indirectly” Dr. Tettamanti answers. The group of Prof. Giacomo Rizzolatti in 1996 identified the mirror neurons in the frontal and parietal areas of the primate and human brain. Mirror neurons are activated when an individual performs an action and when she observes the same action performed by another subject: “Another class of visuo-motor neurons, also described by Prof. Rizzolatti’s group, is also relevant to our study: that is, “canonical neurons”, which are activated both when an individual observes a manipulable object, and when she performs a motor action on it. Mirror neurons and canonical neurons are located in the same brain regions and cooperate in the control and understanding of our and others’ motor actions”.
Finally, we ask Dr. Tettamanti if these unconscious perception-action mechanisms are such that they can be enacted even during sleep: “In deep sleep there is a thalamic suppression of the sensory information sent to the cerebral cortex: however, in some phases of sleep, part of the sensory stimuli can still be processed to some extent (as when, for example, we hear a sound and we end up dreaming of it). For sure, the complex mode of presentation of visual stimuli that we applied in this study cannot be directly used for studies on subjects in a sleep state; however, it may be interesting to use masked stimuli for example in auditory or tactile modalities to study the mechanisms of neural activation in patients in a reduced state of consciousness or in a coma, for the purpose of a better understanding of the pathology of consciousness”.