Behavioural neuroscience
Auditory inhibitory gating in medial prefrontal cortex: Single unit and local field potential analysis

https://doi.org/10.1016/j.neuroscience.2006.03.040Get rights and content

Abstract

Medial prefrontal cortex is a crucial region involved in inhibitory processes. Damage to the medial prefrontal cortex can lead to loss of normal inhibitory control over motor, sensory, emotional and cognitive functions. The goal of the present study was to examine the basic properties of inhibitory gating in this brain region in rats. Inhibitory gating has recently been proposed as a neurophysiological assay for sensory filters in higher brain regions that potentially enable or disable information throughput. This perspective has important clinical relevance due to the findings that gating is dramatically impaired in individuals with emotional and cognitive impairments (i.e. schizophrenia). We used the standard inhibitory gating two-tone paradigm with a 500 ms interval between tones and a 10 s interval between tone pairs. We recorded both single unit and local field potentials from chronic microwire arrays implanted in the medial prefrontal cortex. We investigated short-term (within session) and long-term (between session) variability of auditory gating and additionally examined how altering the interval between the tones influenced the potency of the inhibition. The local field potentials displayed greater variability with a reduction in the amplitudes of the tone responses over both the short and long-term time windows. The decrease across sessions was most intense for the second tone response (test tone) leading to a more robust gating (lower T/C ratio). Surprisingly, single unit responses of different varieties retained similar levels of auditory responsiveness and inhibition in both the short and long-term analysis. Neural inhibition decreased monotonically related to the increase in intertone interval. This change in gating was most consistent in the local field potentials. Subsets of single unit responses did not show the lack of inhibition even for the longer intertone intervals tested (4 s interval). These findings support the idea that the medial prefrontal cortex is an important site where early inhibitory functions reside and potentially mediate psychological processes.

Section snippets

Chronic microelectrode implantation

Animals were anesthetized with xylazine (10 mg/kg) and ketamine (100 mg/kg), and surgery was conducted according to procedures as described in protocols approved by nationally approved guidelines for the care and use of animals (USDA and PHS). All procedures were approved by the Bowling Green State University Animal Care and Use Committee. A stereotaxic apparatus was used for the implantation of recording microwires (NB Laboratories, Denison, TX, USA) into mPFC (A +2.7, M ±0.7, D −3.0)

LFP database

A neuronal database was created for LFP responses. Across the entire set of recording wires, only one positive-going peak was consistently measured to satisfy criteria for significance. This potential, P60, was initially recorded with a 60 ms latency following the onset of tone stimuli (Fig. 1). As indicated in the Experimental Procedures section, LFP responses tone stimuli from each wire were required to be significantly (P<0.01) different in amplitude compared with a 1 s control window that

Discussion

The results of the present study provide direct support for mPFC in sensory IG and show that the inhibition can persist over an extended period at both the LFP and single unit level. These data are critical in order to expand in the analysis of IG toward investigating the functional significance of IG within the mPFC regions. Our general idea related to the functional properties of IG is that each brain region and subregions contain sets of intrinsic inhibitory circuits and these circuits

Acknowledgments

We would like to thank Drs. Jaak Panksepp, Vern Bingman, and William O’Brien for helpful input into the research design of the present study. The work was sponsored by the Bowling Green State University Sponsored Programs and Research Office by Research Incentive Grants to H.C.C. We have also received support from the Department of Psychology at Bowling Green State University. R.P.M. received a J.P. Scott Center for Neuroscience, Mind and Behavior dissertation fellowship that allowed him to

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