Correlation between 50-kHz band activity in primary auditory cortex and social interaction in rats
Hengjun J Kim (Korea Basic Science Institute), Gyunggoo Cho (Korea Basic Science Institute), Youngkyu Song (Korea Basic Science Institute), Song-I Chun (Korea Basic Science Institute), Dongwan Lim (Korea Basic Science Institute), Jeong Kon Kim (Radiology, Asan medical center), Young Ro Kim (Radiology, Massachusetts General Hospital)
Primary auditory cortex (Aud1) of rat is tonotopic, in which spatial divisions of Aud1 corresponds to specific frequency bands. Based on the work of Rutkowski et al. (2003), we created probabilistic maps to display the 50-kHz or 22-kHz band responsivity in Aud1 (Figure A).
Penetrating through the blood-brain barrier, manganese ions (Mn2+) enter and accumulate in the firing neurons via voltage-gated calcium channels, enhancing the MRI signal intensity. Thus, we applied manganese-enhanced magnetic resonance imaging (MEMRI) to investigate the relation between social behavior and 50-kHz band activity in Aud1 using MDEFT pulse sequence (TR/TE=15/3.8ms, Inversion delay=1100ms, 4 segments, FA=15°) and social interaction test (SIT).
First, SIT was performed based on File et al. (1978)’s protocol. Female pairs of rats (6 pairs, n=12) were placed in the box for 10 min and SIT score was measured by the time spent in active social contacts including sniffing, grooming, and following. Secondly, we acquired high-resolution image before and after Mn2+ injection to rats to monitor the brain activity for one day. From the brain activity map and probabilistic map, we calculated Aud1 activities in 50-kHz band region, which were correlated with SIT score.
Figure B showed the relation between brain activities and SIT score for left and right Aud1 regions. Only in the left Aud1, the neural activities receiving 50-kHz band had significant correlation with the SIT score (r=0.70, p=0.01), indicating that animals showing active social behavior had enhanced neural activities to 50-kHz calls in Aud1. Previous behavioral studies showed that the dominant rat had higher SIT score than subordinates, and high SIT score was known to represent low anxiety level. Our result revealed that the animals with low anxiety level had positive bias in the perception of ultrasonic calls. In addition, we suggest that the probabilistic map, if it was applied to functional brain imaging data, could be used to measure the affective valence in the auditory sensory cortex.
RG Rutkowski et al. (2003) Hear. Res. 181, 116-130.
SE File et al. (1978) Br. J. Pharmacol. 62, 19-24.