Mirror neurons and their role in communication

Abstract

Actions done by others are probably the most important stimuli of our lives. Most of others’ actions do not convey intentional information to the observer. From them, however, we understand what others are doing and we can infer why they are doing it. This involuntary communication is fundamental for interpersonal relations, and is at the basis of social life. What is the mechanism underlying our capacity to understand others’ actions? The traditional view is that actions done by others are understood in the same way as other visual stimuli. Thus, action understanding is based on the visual analysis of the different elements that form an action. For example, when we observe a girl picking up a flower, the analyzed elements would be her hand, the flower, and the movement of the hand towards the flower. The association of these elements and inferences about their interaction enables the observer to understand the witnessed action. The discovery of neurons that code selectively biological motion has better specified the neural basis of this recognition mechanism. These theoretical considerations received strong support from the discovery that in the motor cortex of the macaque monkey there is a particular set of neurons that discharge both when the monkey observes a given motor act and when it does the same act. These neurons called “mirror neurons,” represent a system that directly matches observed and executed actions.

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International Journal of Research in Medical Sciences | August 2016 | Vol 4 | Issue 8 Page 3097
International Journal of Research in Medical Sciences
Shete AN et al. Int J Res Med Sci. 2016 Aug;4(8):3097-3101
www.msjonline.org
pISSN 2320-6071 | eISSN 2320-6012
Review Article
Mirror neurons and their role in communication
Anjali N. Shete1*, K. D. Garkal2
INTRODUCTION
Actions done by others are probably the most important
stimuli of our lives. Most of others‟ actions do not
convey intentional information to the observer. From
them, however, we understand what others are doing
and we can infer why they are doing it. This involuntary
communication is fundamental for interpersonal relations,
and is at the basis of social life. What is the mechanism
underlying our capacity to understand others‟ actions?
The traditional view is that actions done by others are
understood in the same way as other visual stimuli.
Thus, action understanding is based on the visual analysis
of the different elements that form an action. For
example, when we observe a girl picking up a flower, the
analyzed elements would be her hand, the flower, and the
movement of the hand towards the flower. The
association of these elements and inferences about their
interaction enables the observer to understand the
witnessed action. The discovery of neurons that code
selectively biological motion has better specified the
neural basis of this recognition mechanism according to
Perrett et al.1 These theoretical considerations received
strong support from the discovery that in the motor cortex
of the macaque monkey there is a particular set of
neurons that discharge both when the monkey observes a
given motor act and when it does the same act. These
neurons called “mirror neurons,” represent a system that
directly matches observed and executed actions.
DISCUSSION
Mirror neurons
In the mid-1990s a new class of premotor neurons was
discovered in the rostral sector of the macaque monkey‟s
ventral premotor cortex, known as area F5. These
ABSTRACT
Actions done by others are probably the most important stimuli of our lives. Most of others‟ actions do not convey
intentional information to the observer. From them, however, we understand what others are doing and we can infer
why they are doing it. This involuntary communication is fundamental for interpersonal relations, and is at the basis
of social life. What is the mechanism underlying our capacity to understand others‟ act ions? The traditional view is
that actions done by others are understood in the same way as other visual stimuli. Thus, action understanding is
based on the visual analysis of the different elements that form an action. For example, when we observe a girl
picking up a flower, the analyzed elements would be her hand, the flower, and the movement of the hand towards the
flower. The association of these elements and inferences about their interaction enables the observer to understand the
witnessed action. The discovery of neurons that code selectively biological motion has better specified the neural
basis of this recognition mechanism. These theoretical considerations received strong support from the discovery
that in the motor cortex of the macaque monkey there is a particular set of neurons that discharge both when the
monkey observes a given motor act and when it does the same act. These neurons called “mirror neurons,” represent a
system that directly matches observed and executed actions.
Keywords: Mirror neurons, Communication, Language
1Department of Physiology, Government medical college, Aurangabad, Maharashtra, India
2Maharashtra University of Health Sciences, Nasik, Maharashtra, India
Received: 12 June 2016
Accepted: 02 July 2016
*Correspondence:
Dr. Anjali N. Shete,
E-mail: dranju01@yahoo.com
Copyright: © the author(s), publisher and licensee Medip Academy. This is an open-access article distributed under
the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial
use, distribution, and reproduction in any medium, provided the original work is properly cited.
DOI: http://dx.doi.org/10.18203/2320-6012.ijrms20162265

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International Journal of Research in Medical Sciences | August 2016 | Vol 4 | Issue 8 Page 3098
neurons discharge not only when the monkey executes
goal-related hand actions like grasping objects, but also
when observing other individuals (monkeys or humans)
executing similar actions. These neurons were called
mirror neurons according to Gallese et al.2 Neurons with
similar properties were later discovered in a sector of the
posterior parietal cortex reciprocally connected with area
F5.
Action observation causes in the observer the automatic
activation of the same neural mechanism triggered by
action execution. The novelty of these findings is the fact
that, for the first time, a neural mechanism that allows a
direct matching between the visual description of an
action and its execution has been identified. Such a
matching system constitutes a parsimonious solution to
the problem of translating the results of the visual
analysis of an observed action-devoid of meaning for the
observer-into an account that the individual is able to
understand. It was proposed that this mechanism could be
at the basis of a direct form of action understanding. If
mirror neurons really mediate action understanding, their
activity should reflect the meaning of the observed
action, not its visual features.
 Mirror neurons in monkeys
 Mirror neuron systems in humans
Mirror neurons in monkeys
Typically, mirror neurons in monkeys do not respond to
the sight of a hand mimicking an action in the absence of
the target. Similarly, they do not respond to the
observation of an object alone, even when it is of interest
to the monkey according to Rizzolatti et al.3 Prompted by
these considerations, two series of experiments were
carried out in which the monkey had no access to the
visual features that normally activate mirror neurons.
The first experiments tested whether the mental
representation of an action triggers F5 mirror neurons, the
second whether the monkeys are able to recognize actions
from their sound. The results of these experiments
provided positive answers to both questions, by showing
that what drives the discharge of mirror neuron is not the
pictorial description of an action, but rather the goal of
the action, or to use a more mentalistic term, the motor
idea of that action according to Rizzolatti et al.3
In the most lateral part of area F5 a population of mirror
neurons related to the execution/observation of mouth
actions was described according to Rizzolatti et al.3 Most
of these neurons discharge when the monkey executes
and observes transitive, object-related ingestive actions,
such as grasping, biting, or licking. However, a small
percentage of mouth-related mirror neurons discharge
during the observation of intransitive, communicative
facial actions performed by the experimenter in front of
the monkey (communicative mirror neurons). Macaque
monkeys seem to have an initial capacity to control and
emit „voluntarily‟ social signals mediated by the frontal
lobe. Most interestingly, this capacity develops in a
cortical area—area F5—that in humans became
Brodmann‟s area 44, a key area for verbal
communication. More recently the role of parietal mirror
neurons in intention understanding has been unveiled.
Fogassi et al described a class of parietal mirror neurons
whose discharge during the observation of an act (e.g.
grasping an object), is conditioned by the type of not yet
observed subsequent act (e.g. bringing the object to the
mouth) specifying the overall action intention.4 This
study shows that parietal mirror neurons, in addition to
recognizing the goal of the observed motor act, allow the
observing monkey to predict the agent‟s next action,
henceforth its overall intention. This neural mechanism
could scaffold more sophisticated mind reading abilities,
as those characterizing our species according to Gallese et
al.5,6
Mirror neuron systems in humans
Several studies using different experimental
methodologies and techniques have demonstrated that a
mirror neuron system matching action perception and
execution also exists in the human brain according to
Rizzolatti et al.3 During action observation there is a
strong activation of premotor and posterior parietal areas,
the likely human homologue of the monkey areas in
which mirror neurons were originally described.
The mirror neuron system for actions in humans is
somatotopically organized, with distinct cortical regions
within the premotor and posterior parietal cortices being
activated by the observation/execution of mouth-, hand-,
and foot-related actions. The mirror neuron system for
actions in humans is directly involved in imitation, in the
perception of communicative actions, and in the detection
of action intentions according to Gallese et al.5
Furthermore, the premotor cortex containing the mirror
system for action is involved in processing action-related
sentences according to Gallese et al suggesting that
mirror neurons together with other parts of the
sensorimotor system could play a relevant role in
language semantics according to Gallese et al.7
Mirror neuron systems also underpin our capacity to
empathize. When we perceive others expressing a given
emotion such as disgust, the same brain areas are
activated as when we subjectively experience the same
emotion. Similar direct matching mechanisms have been
described for the perception of pain according to Gallese
et al.5 These results taken together suggest that our
capacity to empathize with others is mediated by
embodied simulation mechanisms; that is, by the
activation of the same neural circuits underpinning our
own emotional and sensory experiences according to
Gallese et al.5 Recent studies suggest that these
mechanisms could be deficient in individuals affected by
autistic spectrum disorders according to Gallese et al.5

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The discovery of mirror neurons opens new exciting
perspectives in a variety of different fields in social
cognitive neuroscience, like our understanding of
language, ethics and aesthetics according to Freedberg et
al.7
Role of mirror neurons in communication
Communication is a process of exchanging information
via a common system. There are many natural ways in
which individuals may communicate. Besides linguistic
communication, which is at the core of human
communication, humans communicate using arm
gestures, body postures, facial expressions, eye contact,
and head and body movements.
Communication may be intentional and non-intentional.
In both cases, the sender and the receiver of the messages
must have a common code. The difference is that in the
case of intentional communication the sender plays the
leading role and imposes the communication on the
receiver, while in the case of non-intentional
communication, the sender sends the message without
having any intention to do so.
The message is just there. If sender and receiver have a
common code, the message reaches the receiver,
regardless of the will of the sender. Of these two types of
communication, the non-intentional one is the most basic
and primitive. It is evolutionarily necessary because, in
social life, individuals have to understand what others are
doing, whether or not those others intend to be
understood. It is very plausible that intentional
communication is an evolutionarily late development of
non-intentional communication.
Mirror neurons and language
Humans mostly communicate by sounds. Sound-based
languages, however, do not represent the only natural
way for communicating. Languages based on gestures
(signed languages) represent another form of complex,
fully structured communication system. By using sign
language, people express abstract concepts, learn
mathematics, physics, philosophy, and even create poetry
according to Corballis et al.7
Nonetheless, the fact that signed languages represent a
fully structured communication system has not changed
the view, which many share, that speech is the only
natural human communication system, and that the
evolutionary precursor of human speech consists of
animal calls. Humans emit sound to communicate;
animals emit sounds to communicate, therefore human
speech evolved from animal calls. The logic of this
syllogism is rather shaky. Its weakness becomes apparent
when one examines animal calls and human speech more
closely. First, the anatomical structures underlying
primate calls and human speech are different. Primate
calls are mostly mediated by the cingulate cortex and by
deep, diencephalic and brain stem structures according to
Jürgens.8 In contrast, the circuits underlying human
speech are formed by areas located around the Sylvian
fissure, including the posterior part of IFG. It is hard to
imagine how in primate evolution, the call system shifted
from its deep position found in non-human primates to
the lateral convexity of the cortex where human speech is
housed.
Second, speech in humans is not, or is not necessarily,
linked to emotional behavior, whereas animal calls are.
Third, speech is mostly a dyadic, person-to-person
communication system. In contrast, animal calls are
typically emitted without a well-identified receiver.
Fourth, speech is endowed with combinatorial properties
that are absent in animal communication.
As Chomsky et al rightly stressed, human language is
“based on an entirely different principle” from all other
forms of animal communication.9 finally, humans do
possess a “call” communication system like that of
nonhuman primates and its anatomical location is similar.
This system mediates the utterances that humans emit
when in particular emotional states (cries, yelling, etc.).
These utterances, which are preserved in patients with
global aphasia, lack the referential character and the
combinatorial properties that characterize human speech.
The advocates of the sound-based theory of language
origin consider a strong argument in favour of this theory
to be the presence of referential information in some
animal calls according to Pinker et al.10 The famous study
of the alarm calls of vervet monkeys according to Cheney
et al, as well as other studies that extended these
observations to other species and other communicative
contexts (social relationship, food, inter-group
aggression), showed that evolution tried this pathway.11
The reason why this attempt did not succeed is the lack of
flexibility inherent in any communicative system based
on emotions. In a non-emotional communication system
the same word, for example the word fire, which is
basically an alarm message (“escape”), may assume a
completely different meaning. It may indicate, for
example, that the fire is ready and we can start to cook
our meal (“approach message”), as well as conveying
other positive messages.
This flexibility cannot occur in an emotional
communicative system because a referential meaning
cannot indicate a behavior that is in contrast with the
emotion that generated it. Thus the same utterance or call
cannot convey, in different contexts, an escape and an
approach message. If not animal calls, what could be the
origin of human speech? An alternative hypothesis is that
the path leading to speech started with gestural
communication. This hypothesis, first proposed by the
French philosopher Condillac, has recently found several
defenders according to Armstrong et al; Corballis.12,13
According to this theory, the initial communicative

Shete AN et al. Int J Res Med Sci. 2016 Aug;4(8):3097-3101
International Journal of Research in Medical Sciences | August 2016 | Vol 4 | Issue 8 Page 3100
system in precursors of modern humans was based on
very simple, elementary gesturing. Sounds were then
associated with the gestures and became progressively
the dominant way of communication.
The discovery of mirror neurons provided strong support
for the gestural theory of speech origin. Mirror neurons
create a direct link between the sender of a message and
its receiver. Thanks to the mirror mechanism, actions had
done by one individual become messages that are
understood by an observer without any cognitive
mediation. The observation of an individual grasping an
apple is immediately understood because it evokes the
same motor representation in the parieto-frontal mirror
system of the observer. Similarly, the observation of a
facial expression of disgust is immediately understood
because it evokes the same representation in the
amygdala of the individual observing it according to
Gallese et al.3
On the basis of this fundamental property of mirror
neurons, and the fact that the observation of actions like
hand grasping activates the caudal part of IFG (Broca‟s
area), Rizzolatti et al proposed that the mirror mechanism
is the basic mechanism from which language evolved.14
In fact, the mirror mechanism solved, at an initial stage of
language evolution, two fundamental communication
problems: parity and direct comprehension.
Thanks to the mirror neurons, what counted for the
sender of the message also counted for the receiver. No
arbitrary symbols were required. The comprehension was
inherent in the neural organization of the two individuals.
A criticism of this view is based on the fact that the
monkey mirror neuron system is constituted of neurons
coding object-directed actions. Thus, the monkey mirror
neuron system forms a closed system, which by
definition does not appear to be particularly suitable for
intentional communication.
Yet, if this is true for the monkey, it is not the case for the
human mirror system. As reviewed above, TMS and
brain imaging studies have shown that activation of the
human mirror system is achieved by presentation of
intransitive actions according to Fadiga et al, Maeda et al,
as well as during pantomime observation according to
(Buccino et al, Grèzes et al.15-18 It is difficult to specify
how the shift from a closed system of monkeys to an
open, intentionally communicative system, in humans
might have occurred.
The view, however, that communicative actions derived
from a more ancient system of non-communicative
gestures is not new. Van Hoof for example, proposed
that many of the most common communicative gestures
of the monkey, such as lip smacking, are ritualizations of
ingestive actions that monkeys use for affiliative
purposes.19 The fact that mouth mirror neurons respond
both to the observation of communicative actions and
during the execution of ingestive actions appears to give
a neurophysiological basis to this idea according to
Ferrari et al.20 Similarly, Vygotsky suggested that
intransitive actions derive in children from object-
directed transitive actions.21 For example, when objects
are located close to a child, the child grasps them. When
they are located far from the child, the child extends his
or her hands towards the objects. Because the mother
understands this gesture, the child uses it again and again
and, eventually, attempts to reach objects become
communicative gestures. Thus, the transition from object-
directed to intentional communicative gesture can be
accommodated by the mirror neuron hypothesis of
language evolution.
The discovery of mirror neurons opens new exciting
perspectives in a variety of different fields in social
cognitive neuroscience, like our understanding of
language, ethics and aesthetics.
Funding: No funding sources
Conflict of interest: None declared
Ethical approval: Not required
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Cite this article as: Shete AN, Garkal KD. Mirror
neurons and their role in communication. Int J Res
Med Sci 2016;4:3097-101.