Mirror Neuron - Doubts Concerning Mirror Neurons

Doubts Concerning Mirror Neurons

Although many in the scientific community have expressed excitement about the discovery of mirror neurons, there are scientists who have expressed doubts about both the existence and role of mirror neurons in humans. According to scientists such as Hickok, Pascolo and Dinstein it is not clear whether mirror neurons really form a distinct class of cells (as opposed to an occasional phenomenon seen in cells that have other functions), and whether mirror activity is a distinct type of response or simply an artifact of an overall facilitation of the motor system.

In 2008, Ilan Dinstein et al. argued that the original analyses were unconvincing because they were based on qualitative descriptions of individual cell properties, and did not take into account the small number of strongly mirror-selective neurons in motor areas. Other scientists have argued that the measurements of neuron fire delay seem not to be compatible with standard reaction times, and pointed out that nobody has reported that an interruption of the motor areas in F5 would produce a decrease in action recognition. (Critics of this argument have replied that these authors have missed human neuropsychological and TMS studies reporting disruption of these areas do indeed cause action deficits without affecting other kinds of perception.)

In 2009, Lingnau et al. carried out an experiment in which they compared motor acts that were first observed and then executed to motor acts that were first executed and then observed. They concluded that there was a significant asymmetry between the two processes that indicated that mirror neurons do not exist in humans. They stated "Crucially, we found no signs of adaptation for motor acts that were first executed and then observed. Failure to find cross-modal adaptation for executed and observed motor acts is not compatible with the core assumption of mirror neuron theory, which holds that action recognition and understanding are based on motor simulation."

In 2009, Greg Hickok published an extensive argument against the claim that mirror neurons are involved in action-understanding: "Eight Problems for the Mirror Neuron Theory of Action Understanding in Monkeys and Humans." He concluded that "The early hypothesis that these cells underlie action understanding is likewise an interesting and prima facie reasonable idea. However, despite its widespread acceptance, the proposal has never been adequately tested in monkeys, and in humans there is strong empirical evidence, in the form of physiological and neuropsychological (double-) dissociations, against the claim."

Neurophilosophers such as Patricia Churchland have expressed both scientific and philosophical objections to the theory that mirror neurons are responsible for understanding the intentions of others. In chapter 5 of her 2011 book, Braintrust, Churchland points out that the claim that mirror neurons are involved in understanding intentions (through simulating observed actions) is based on assumptions that are clouded by unresolved philosophical issues. She makes the argument that intentions are understood (coded) at a more complex level of neural activity than that of individual neurons. Churchland states that "A neuron, though computationally complex, is just a neuron. It is not an intelligent homunculus. If a neural network represents something complex, such as an intention, it must have the right input and be in the right place in the neural circuitry to do that".

Recently, Cecilia Heyes (Professor of Experimental Psychology, Oxford) has advanced the theory that mirror neurons are the byproduct of associative learning as opposed to evolutionary adaptation. She argues that mirror neurons in humans are the product of social interaction and not an evolutionary adaptation for action-understanding. In particular, Heyes rejects the theory advanced by V.S. Ramachandran that mirror neurons have been "the driving force behind the great leap forward in human evolution".(Ramachandran, 2000)