ABSTRACT
In 1979, Gibson first advanced the idea that the sight of graspable objects automatically activates in the observer the repertoire of actions necessary to interact with them, even in the absence of any intention to act ("affordance effect"). The neurophysiological substrate of this effect was later identified in a class of bimodal neurons, the so-called "canonical" neurons, located within monkey premotor cortex. In humans, even if different behavioral studies supported the existence of affordance effect, neurophysiological investigations exploring its neural substrates showed contradictory results. Here, by means of Transcranial Magnetic Stimulation (TMS), we explored the time-course of the "affordance effect" elicited by the observation of everyday-life graspable objects on motor cortex of resting observers. We recorded motor evoked potentials (MEP) from three intrinsic hand muscles (two "synergic" for grasping, OP and FDI and one "neutral", ADM). We found that objects' vision determined an increased excitability at 120 milliseconds after their presentation. Moreover, this modulation was proved to be specific to the cortical representations of synergic muscles. From an evolutionary perspective, this timing perfectly fits with a fast recruitment of the motor system aimed at rapidly and accurately choosing the appropriate motor plans in a competitive environment filled with different opportunities.
Subject(s)
Evoked Potentials, Motor/physiology , Hand Strength/physiology , Motor Cortex/pathology , Motor Neurons/physiology , Muscle, Skeletal/physiology , Transcranial Magnetic Stimulation/methods , Adult , Female , Hand/physiology , Humans , Male , Young AdultABSTRACT
Chemical inertness of typical styrene polymers used in food packaging was investigated by "global migration" measurements. Absorption of liquid food simulants by plastics was also studied. Migrated compounds, detected and identified by gaschromatography-mass spectrometry (GC-MS), are styrene (monomer) and styrene dimers. All migration values, measured under different experimental conditions, turn out to be lower than the overall migration limit, as fixed by current legislation.
