Mirror Neurons in a New World Monkey, Common Marmoset.

Wataru Suzuki,Naohisa Miyakawa,Hiroshi Abe,Noritaka Ichinohe,Taku Banno,Naokazu Goda

doi:10.3389/fnins.2015.00459

Abstract

Mirror neurons respond when executing a motor act and when observing others' similar act. So far, mirror neurons have been found only in macaques, humans, and songbirds. To investigate the degree of phylogenetic specialization of mirror neurons during the course of their evolution, we determined whether mirror neurons with similar properties to macaques occur in a New World monkey, the common marmoset (Callithrix jacchus). The ventral premotor cortex (PMv), where mirror neurons have been reported in macaques, is difficult to identify in marmosets, since no sulcal landmarks exist in the frontal cortex. We addressed this problem using “in vivo” connection imaging methods. That is, we first identified cells responsive to others' grasping action in a clear landmark, the superior temporal sulcus (STS), under anesthesia, and injected fluorescent tracers into the region. By fluorescence stereomicroscopy, we identified clusters of labeled cells in the ventrolateral frontal cortex, which were confirmed to be within the ventrolateral frontal cortex including PMv after sacrifice. We next implanted electrodes into the ventrolateral frontal cortex and STS and recorded single/multi-units under an awake condition. As a result, we found neurons in the ventrolateral frontal cortex with characteristic “mirror” properties quite similar to those in macaques. This finding suggests that mirror neurons occur in a common ancestor of New and Old World monkeys and its common properties are preserved during the course of primate evolution.

Highlights

Mirror neurons are cells that respond both when performing a motor act and when observing others performing a similar act
We showed mirror neurons responsive to grasping action found in Old world monkeys exist in New world monkeys, indicating that the evolution of mirror neurons can be traced to a common ancestor of Old and New world monkeys with primate specific motor repertories such as reaching, grasping, and manipulation actions with hands (Cartmill, 1974; Bloch and Boyer, 2002; Stepniewska et al, 2005)
We found that the injection site in superior temporal sulcus (STS) located in a ventral part of the fundus of the superior temporal area (FSTv), and the labeled cells were distributed in the ventrolateral frontal cortex including area 6V which is comparable to macaque F4/5 (Burman et al, 2008; Paxinos et al, 2012) where mirror neurons were found, area 8A and area 12L/45 (Figure 1C)

Summary

INTRODUCTION

Mirror neurons are cells that respond both when performing a motor act (such as grasping, breaking, or tearing) and when observing others performing a similar act. Mirror neurons are suggested to be involved in the understanding of others’ action and intention and in imitation (Gallese et al, 1996; Iacoboni et al, 1999; Rizzolatti et al, 2001), by forming a link between the sensory description and the individual motor representation (Rizzolatti and Craighero, 2004), and may be a neural substrate of language evolution (Rizzolatti and Arbib, 1998) They have been found in the ventral premotor cortex (PMv) and inferior parietal lobule (Rizzolatti and Craighero, 2004; Ferrari et al, 2009). We simultaneously recorded multiunits from a part of the STS containing cells responsive to the sight of others’ action, which was determined by multiunit recording beforehand, and from a circumscribed area in the frontal cortex, which was identified in vivo to have cells fluorescently labeled by a retrograde tracer that had been injected to the STS site after the first recording

MATERIALS AND METHODS

RESULTS

DISCUSSION