Focus

Sex differences in neural coding of goal-directed actions in the human "mirror neurons" system

To investigate the existence in human beings of the "mirror neurons" originally found in monkeys by means of single cell recordings, Alice Mado Proverbio and Federica Riva at the University of Milan-Bicocca, together with Alberto Zani at the Institute of Molecular Bioimaging and Physiology (IBFM) of CNR at Milan, recorded brain electrical potentials in a group of volunteers. Now in print in Neuropsychologia, the findings of the present study point out the neuronal processes going on in our brain when we observe "incongruent" actions, thus inducing us to not imitate or "mirror" it at all.
"It is renown", Alice Mado Proverbio explains, "that goal-directed actions, such as to pick a ripe fruit to eat it, cause a greater activation of the fronto-parietal "mirror neurons" system (including the inferior frontal gyrus, the left inferior parietal lobule, and the superior temporal sulcus, STS) than non-goal directed or less salient actions, such as reaching a fruit but not picking it or picking it and throwing it away." "It seems, then, that premotor and somatosensory neural populations exist involved both in the observation of other agents' goal-directed actions, and in imitation, identification, and learning."
Mado Proverbio and her colleagues sought for the existence of this functional system in 23 male and female college students showing them visual images while recording brain activity elicited by these images by means of 128 bioelectrical sensors, a technique defined as "event-related potentials" (ERPs) of the brain.
Hundreds of images portraying people engaged in ordinary behavioural actions of the human beings (e. g., to take a bath, to write a letter, to make a toast, etc.) as compared to many others portraying senseless or non-goal directed actions (e. g., a businessman sucking oil with a straw from a car engine, an elegant lady standing up on one foot only in a desert, a guy opening a boiled egg with an ace, etc.).
"To the sample group", Mado Proverbio continued " was not required to evaluate the appropriateness of the scenes portraying the human beings, but to respond to images portraying urban and/or natural landscapes intermixed with the other images, shown as well. This had the goal to avoid decision-making processes driven by subjective variables such as, for instance, ethical or moral instances. The findings pointed out the automatic recognition, mostly in the female brain, of the goal-directed images, and the distinction of the congruent actions from the incongruent ones, just starting from 170-200 milliseconds post-stimulus, thus indicating a faster processing of socially- and emotionally-charged information in the latter sex.
Intracortical source reconstruction of the bioelectrical activity by means of LORETA indicated that during the recognition of congruent and sound actions the regions of the brain being more active included the infero-parietal areas (BA40), the left inferior frontal gyrus, the motor and premotor areas (BA4 and BA 6), the STS, and the visual extra-striate cortices (involved in human face and body coding.)
After about 450-600 ms, the peak of a negative response to the images of unexpected and inappropriate actions could be seen, with a closer emotional characterization of such a response in females (i. e., Cingulate cortex, limbic system, and STS), and a more rational characterization in males (i. e., orbito-frontal cortex and STS.)" Hence, the data "suggest a greater sensitivity of females brain to actions congruity", Mado Proverbio concluded "and provide new evidence of the existence of the "mirror neurons" system in the human beings also (besides in the primates), and of their role in the social complex behaviours of imitation, learning, and evaluation of others' behaviour.

March 3rd, 2010

The Card:
Who: Cognitive Electrophysiology Laboratory of the University of Milan-Bicocca, Institute of Molecular Bioimaging and Physiology of CNR, Segrate (MI)

What: A study on the undertanding of neuronal processes during the observation of congruent and incongruent actions, now in print in Neuropsychologia 2010.

For informations: Alice Mado Proverbio, Cognitive Electrophysiology Laboratory of the University of Milan-Bicocca, tel. 02/64483755; e mail: mado.proverbio@unimib.it


Source: Proverbio, A. M., et al. When neurons do not mirror the agent's intentions: Sex differences in neural coding of goal-directed actions. Neuropsychologia, 48 (2010), 1454-1463.