Shakespeare's mirror was technically primitive, yet somehow he could see deep into the truth.
Poetry is emotion recollected in tranquility sayeth an old literary giant. An article in the latest Current Directions in Psychological Science takes that a step further and says all of language consists of a respit from emotional control. Two Italian neuroscientists, Leonardo Fogassi and Pier Francesco Ferrari, argue in “Mirror Neurons and the Evolution of Embodied Language” (abstract here) that a central difference between animal cries and human speech is that the cries are under the control of the brain’s emotional circuitry while speech is part of the perceptual (sensori-motor) apparatus.
call production is nonhuman primates is correlated with intense emotional states, with the main function being to signal urgent or imminent events. [p. 136]
There is no apparent evolutionary linkage between the part of the brains monkeys and apes use when they vocalize and the brains of humans when we speak. Monkey calls are ‘under the neural control of the primitive [sic] limbic circuit” while ape gestues and human speech is subject to a “sophisticated” capacity to “voluntarily control goal-directed actions.”
This blog has discussed many traits indicating that speech is not an expansion of animal vocalizations, and the Fogassi-Ferrari piece is further confirmation of the point. Their article goes on to ask, well, if speech is not dependent on the areas that control animal vocalization, what part of the ape brain was adapted to permit speech?
A critical part of the human brain for producing speech is known as Broca’s area. People who suffer strokes can still understand much of what is said to them, but have great difficulty speaking. Fogassi-Ferrari assert that monkey brains use a homologous region known as F5. Obviously monkeys do not use region F5 to speak, but it is important in both hand and mouth actions. Imaging studies of the human brain have shown that, besides controlling speech, Broca’s area is involved in a variety of hand-dependent tasks. There are other important similarities as well. Monkey region F5 and Broca’s area are activated
- when subjects observe others performing goal-directed actions with their hands or mouth,
- or when hearing sounds that are associated with actions,
- or when an individual observes another’s mouth movements, even without hearing any sound.
Broca’s area, of course, include functions not found in monkeys. For instance, reading about actions [e.g., “He grasps the glass”] activates Broca’s area.
Both the F5 region of monkey brains and human Broca’s area contain “mirror neurons,” i.e., neurons that fire when an individual either performs an action or perceives another perform that same action. There are regions in a monkey’s brain that fire when the monkey performs a hand action or sees another monkey perform a matching hand action. Mirror neurons are particularly important in goal-directed actions. Thus, the same neurons are activated if I perform a task in pursuit of goal Y or if I see another individual act in pursuit of goal Y. Most impressively, if a hand action is identical when pursuing either goal Y or goal Z, my goal Y mirror neurons do not activate if I see you perform that hand action while pursuing goal Z. For this kind of distinction to exist at the neuronal level, the observer monkey must truly understand the reasons another monkey acts as it does.
Mirror neurons are critical to making sense of the world. They allow one individual to interpret perceptions in terms of the individuals own experiences. Without this sympathy, responses to the world would be, at best, emotional: sound — fear — flight. With mirrored experience you can have a more measured reaction: sound — recognition — action appropriate to circumstances.
In cases where a perception produces a strong emotional reaction — e.g., fear or rage — reflexive brain regions dominate. It is in the less emotionally charged situations that mirror neurons can contribute to understanding and action. Friendly gestures and tone that lower the emotional strength of the moment make understanding more possible. For many generations, people have know this importance of emotional calm, but it is still satisfying to have it explained at the neuronal level. Mirror neurons cannot keep in sympathetic contact with their environment if fearful, angry, or defensive emotions override them.
Mirror neurons are also valuable in learning by observing and imitating. This arrangement suggests a possible solution to the mystery of how children manage to reproduce the verbal sounds they hear others make. (I am straying a bit from Fogassi-Ferrari at this point, inserting a bit of my own speculation inspired by reading the article.) Mirror neurons may fire when infants babble, providing a neuronal distinction between the sounds of, say, ma and doh. Then, when a child hears donut, the doh mirror fires, so when the child tries speaking the world it begins with doh.
Mirror neurons also make the interchangeability of speaker-listener roles seem perfectly natural. Speaking Pass the salt, please fires the same mirror neurons as listening to the sentence, so, neurologically speaking, the speaker and listener roles have much in common.
None of this analysis explains the selective pressures that led to the rise of speech, but it provides a neurological basis for insisting on many of the points that recur on this blog.
- Speech is fundamentally different in nature and function from animal vocalizations, using different circuits and neuron types.
- Listening requires a sympathetic relationship with the speaker, a relationship automatically supported by the mirror neurons in Broca’s area.
- The speaker-listener roles in the communication triangle are fundamentally interchangeable in the natural way that Broca’s area mirror neurons allow.
- Both speaking and listening are voluntary rather than emotional and follow sensori-motor pathways rather than emotional circuits.
If you want to argue, say, that human communications are extensions of animal vocalizations, or that listening does not require sympathy, or that speaking and listening are separate states, or that meaning arises from the symbols rather than the voluntary attentional state, you are going to have to explain how the neurological evidence is irrelevant, misleading, or just plain wrong.