According to Jean Piaget, a 7-8 year-old child succeeds in a conservation of number task
since he understands that two rows contain an equal number of objects even if they differ in length
(because the objects in one of the rows have been spread apart). To succeed in such a task, it was
proposed that the visuospatial interference is overcame thanks to the inhibition of the
"length=number" strategy. Here, we propose that neural traces of that developmental stage persist in
the adult brain. In this perspective, we conducted neuro-imaging studies on a Piaget-like task in
young adults.
After a bibliographical state of art about the numerical abilities across cognitive
development, the neural bases of cognitive inhibition and numerical processes, two experiments are
presented. A first experiment using event-related potentials, in a first session, shows that the
inhibition of the number/length interference, contrasted to a control condition of covariation, elicits
electrophysiological waves typical of inhibition (N2 and P3). In a second session, the fMRI data
recorded from the same subjects show that such an inhibition recruits posterior heteromodal areas.
A second experiment using fMRI (without previous EEG session) also points out the role of the
anterior cingulate cortex, known to be involved in inhibitory control (namely, conflict monitoring,
error detection). Bilateral parietal areas for counting or mental/spatial manipulation are also
activated in this numerical Piaget-like task.
In conclusion, our work confirms that in adult's brain, any of the perceptual biases of early
childhood might not have been fully overcame or at least that their inhibition requires a
neurocognitive cost.