How the brain turns a picture into motion, and motion into sound

 

The lecture took place at the 3^rd International Conference ‘Neurobiology of language and speech’.

Two streams of perception

Discussing the perception of information by the brain, Luciano Fadiga presented the hypothesis of two streams: ventral and dorsal. These are two brain systems which work in parallel and codify visual information. During the visual recognition of objects, the information is first fixed in the primary visual cortex and then in the secondary visual cortex, where the ventral and dorsal streams originate.

The ventral stream runs to the temporal lobe, the dorsal – to the parietal lobe of the cerebral cortex. Experiments on monkeys with brain lesions in the temporal and parietal lobes helped to form a hypothesis on the role of these brain regions in the perception of visual information. Thus, the temporal lobe is involved in memory formation and is charged with the task of being a kind of ‘archive’, where information is categorised. The parietal lobe is responsible for spatial orientation. According to the hypothesis, the ventral stream is in charge of semantics – answering the question ‘what is it?’, while the dorsal stream answers questions about spatial position, processing such concepts as ‘where?’ and ‘how?’.

Our brain is a classifying machine. It categorises everything that we see into numerous categories. The brain establishes associations, links between objects and concepts, grouping objects according to different parameters.

Luciano Fadiga, Professor of the University of Ferrara (Italy)

‘A brick, for example, belongs to the conceptual category of construction materials, and yet it can be included into the same group as a red apple based on its colour. We do it automatically, without thinking. It’s our brain that does it’, said Luciano Fadiga. 

Motion and action

Luciano Fadiga said that after processing visual information the brain makes decisions about further operations. For example, if a person understands that he needs the object he sees, he stretches his arm to take it. At the same time, his brain should be able to realise quickly if there is an obstacle in the way, and how he should clasp his hand to grasp the object he desires. Luciano Fadiga has studied with his colleagues the functioning of the monkey brain when monkeys were using their limbs grasping objects of different sizes and shapes. They managed to record their brain reactions and the mechanisms that lead to motion.

Motion, according to the definition provided by the scientists, is a hierarchical sequence of moves to achieve a specific goal. If the goal is to grasp a visible object, then grasping will be the motion carried out through a sequence of moves controlled by the brain. According to the data obtained by the scientists, decision making happens in the ventral premotor cortex (F5 area). This is the area where the team of researchers from Parma, including Luciano Fadiga, managed to record mirror neurons.

It was a chance that led to the first steps in discovering mirror neurons.

‘My colleague was eating ice-cream in the lab. While he was licking an ice-cream, the F5 area of the brain of a test monkey, which was put on an encephalograph, demonstrated the reaction which would happen if the monkey itself was producing the movement similar to the actions of my colleague. The monkey, however, remained still at that moment,’ said the scientist.

Thus, it was found that neurons in the F5 area are activated not only when grasping an object, but also during action observation.

Broka area

Luciano Fadiga thinks that all the factors discussed above, affect human speech production. The scientist is sure that visual recognition, followed by the processing of information into the motion of speech organs activates speech production. In other words, sounds do not have a crucial role, according to the scientist. ‘Listen to how an old man and a child or people with different accents pronounce the same word: the sounds may vary, but the movements of lips and tongue will be similar,’ he stressed.

No doubt, the brain of a human being and the brain of a monkey differ significantly: a monkey does not use the language in the usual sense of the word. At the same time, Luciano Fadiga thinks that there are similarities between the brain of a monkey and the brain of a human being, the latter having advanced significantly in the process of evolution.

Luciano Fadiga thinks that the Broka area (or Broka centre) in the human brain can be a cytoarchitectonic homologue of the F5 area of a monkey. The Broka area is located in the inferior posterior part of the prefrontal cortex and is responsible for sensorimotor organisation of speech. According to the research, the Broka area is activated during speech recognition and production, mathematical calculations, listening to music, and logical operations. Processes in the Broka area, the scientist thinks, are also connected with the visual perception of the world around: visual analysis helps a person to plan and make predictions of his own actions and actions of other people. Luciano Fadiga is sure that it is one of the most important evolutionary developments which made it possible for people to operate with the concept of future, make long-term plans, understand the consequences of their actions, develop symbolic thinking and, possibly, language.

‘Having paid the price for efficiency, our species obtained new opportunities: invented new actions and reactions, searched for new solutions. All this is implemented through an extremely complex sensorimotor mechanism, whose computational capabilities could be used for learning purposes, too,’ concluded Luciano Fadiga.