Short review: L. Shapiro, Making sense of mirror neurons, Synthese (2009) 167, pp. 439-456.
(a) Thesis: Mirror neuron system (MNS) is a component of a sensory system (a sixth sense, so to speak) that has the function to perceive actions.
(b) Experimental setting:
Experiment 1: Data concerning cell’s receptive field is important to establish the properties of cells involved in neural processing. These data is displayed in the form of a tuning curve. The tuning curve illustrates how the cell responds to a certain stimuli (sound, visual etc.). Mirror neuron function can be measured using a tuning curve. The experiment consisted in measuring the tuning curve of three mirror neurons in a monkey. One mirror neuron was more sensitive to the action of grasping an object with an intention to eat, another was more sensitive to the action of grasping an object with an intention to place it in a container. The third mirror neuron did not discriminate between the two actions.
Experiment 2: Two clusters of mirror neurons in humans were studied using a fMRI. With an increased exposure to the stimulus, which was a movie showing a human hand grasping an object, the tuning curves derived from the activity of these two clusters of mirror neurons were systematically flattening.
Experiments revealed that mirror neurons possess similar features to cells involved in processing sense data. First experiment showed that mirror neurons distinguish between actions carried out with different intentions. Cells involved in processing sense data also have an “ability” to distinguish between different aspects of the same category of stimuli (e.g. discrimination between colours which fall into the category of visual stimuli). Second experiment revealed that mirror neurons show the effects of habituation when exposed to repetition of the same stimuli. Cells involved in the processing sense data also show effects of habituation in such circumstances. The results of these experiments reinforce the thesis that MNS functions as a sense, similar in some aspects to other senses. What differentiates this particular sense from others is, above all, it’s object which is an action.