Do monkey F 5 mirror neurons show changes in firing rate during 1 repeated observation of natural actions ?

23 24 Mirror neurons were first discovered in area F5 of macaque monkeys. In humans, 25 non-invasive studies have demonstrated an increased BOLD signal in homologous 26 motor areas during action observation. One approach to demonstrating that this 27 indicates the existence of mirror neurons in humans has been to employ fMRI 28 adaptation to test whether the same population of neurons is active during both 29 observation and execution conditions. Although a number of human studies have 30 reported fMRI adaptation in these areas a recent study has shown that macaque mirror 31 neurons do not attenuate their firing rate with two repetitions. Here we investigated 32 whether mirror neurons modulate their firing rate when monkeys observed the same 33 repeated natural action multiple times. We recorded from 67 mirror neurons in area 34 F5 of two macaque monkeys while they observed an experimenter perform a reach-to35 grasp action on a small food reward using a precision grip. Although no changes were 36 detectable for the first two repetitions, we show that both the firing rate and the 37 latency at which mirror neurons discharged during observation were subtly modulated 38 by the repetition of the observed action over 7-10 trials. Significant adaption was 39 mostly found in the period immediately before the grasp was performed. We also 40 found that the local field potential activity in F5 (beta frequency range, 16-23 Hz), 41 that is attenuated during action observation, also showed systematic changes with 42 repeated observation. These LFP changes occurred well in advance of the mirror 43 neuron adaptation. We conclude that macaque mirror neurons can show intra-modal 44 adaptation, but whether this is related to fMRI adaptation of the BOLD signal requires 45 further investigation. 46 47 48 49 50