The Journal of Neurophysiology Vol. 77 No. 6 June 1997, pp. 2945-2965
Copyright ©1997 The American Physiological Society

Regularity of Firing of Neurons in the Inferior Colliculus

Adrian Rees, Ali Sarbaz, Manuel S. Malmierca, and Fiona E. N. Le Beau

Department of Physiological Sciences, The Medical School, University of Newcastle upon Tyne, NE2 4HH, United Kingdom

Rees, Adrian, Ali Sarbaz, Manuel S. Malmierca, and Fiona E. N. Le Beau. Regularity of firing of neurons in the inferior colliculus. J. Neurophysiol. 77: 2945-2965, 1997. The spike discharge regularity of 254 tonically firing units in the inferior colliculus (IC) of the anesthetized guinea pig was studied in response to tones presented at best frequency (BF) to the ear contralateral to the recorded IC. Regularity of firing was measured by calculating the coefficient of variation (CV) as a function of time over the course of a unit's response. Two hundred and fifteen units (56 under urethan and 159 under chloralose anesthesia) in the central nucleus of the IC (CNIC) were studied in detail. In response to tones at 15-25 dB above threshold, 80% of units in the urethan sample fired regularly (CV < 0.5) during their sustained response, and 46% were highly regular (CV  0.35). For chloralose the values were 68% and 23%, respectively. Units recorded under urethan were significantly more regular than those recorded under chloralose. For units in the sample with a measurable onset CV, 63% were regular and 44% highly regular under urethan, and 73% were regular and 54% highly regular under chloralose. The units' peristimulus time histogram (PSTH) patterns were classified into subdivisions of four categories: choppers [9%: chop-sustained (C_s), chop-onset (C_o)]; pausers [42%: pauser-chop-sustained(P/C_s), pauser-chop-onset (P/C_o), pauser-no-chop]; ON-sustained(43%: primary-type, L-type, h-type); and sustained (6%). The presence of chopping was a reliable predictor of regularity: C_s and P/C_s units were highly regular throughout their response, whereas C_o and P/C_o units were highly regular at onset and became less regular. Some units in the other PSTH categories were highly regular despite the absence of chopping, and units with virtually identical PSTHs showed very different sustained CVs. Regularity was measured as a function of firing rate in 71 units. In 23%, regularity remained constant when firing rate changed with stimulus level. Forty-six percent fired more regularly as firing rate increased, 8% fired less regularly, and 23% of units showed no consistent relationship between CV and firing rate. Regularity did not correlate with the neurons' frequency response areas or BFs. Regular firing was also found in a smaller sample of units recorded in cortices surrounding the CNIC. We conclude that regular firing is a characteristic feature of most neurons in the IC. Regularity is a specific feature correlated with four PSTH types (C_s, C_o, P/C_s, and P/C_o). Other PSTH types may or may not exhibit regularity.

This article has been cited by other articles:

				M. S. Malmierca, M. A. Izquierdo, S. Cristaudo, O. Hernandez, D. Perez-Gonzalez, E. Covey, and D. L. Oliver A Discontinuous Tonotopic Organization in the Inferior Colliculus of the Rat J. Neurosci., April 30, 2008; 28(18): 4767 - 4776. [Abstract] [Full Text] [PDF]

				M. Xu, C. H. Liu, Y. Xiong, and J. He Corticofugal modulation of the auditory thalamic reticular nucleus of the guinea pig J. Physiol., November 15, 2007; 585(1): 15 - 28. [Abstract] [Full Text] [PDF]

				M. L. Tan and J.G.G. Borst Comparison of Responses of Neurons in the Mouse Inferior Colliculus to Current Injections, Tones of Different Durations, and Sinusoidal Amplitude-Modulated Tones J Neurophysiol, July 1, 2007; 98(1): 454 - 466. [Abstract] [Full Text] [PDF]

				M. L. Tan, H. P. Theeuwes, L. Feenstra, and J.G.G. Borst Membrane Properties and Firing Patterns of Inferior Colliculus Neurons: An In Vivo Patch-Clamp Study in Rodents J Neurophysiol, July 1, 2007; 98(1): 443 - 453. [Abstract] [Full Text] [PDF]

				L.-F. Liu, A. R. Palmer, and M. N. Wallace Phase-Locked Responses to Pure Tones in the Inferior Colliculus J Neurophysiol, March 1, 2006; 95(3): 1926 - 1935. [Abstract] [Full Text] [PDF]

				D. Perez-Gonzalez, M. S. Malmierca, J. M. Moore, O. Hernandez, and E. Covey Duration Selective Neurons in the Inferior Colliculus of the Rat: Topographic Distribution and Relation of Duration Sensitivity to Other Response Properties J Neurophysiol, February 1, 2006; 95(2): 823 - 836. [Abstract] [Full Text] [PDF]

				P. X. JORIS, C. E. SCHREINER, and A. REES Neural Processing of Amplitude-Modulated Sounds Physiol Rev, April 1, 2004; 84(2): 541 - 577. [Abstract] [Full Text] [PDF]

				D. Suta, E. Kvasnak, J. Popelar, and J. Syka Representation of Species-Specific Vocalizations in the Inferior Colliculus of the Guinea Pig J Neurophysiol, December 1, 2003; 90(6): 3794 - 3808. [Abstract] [Full Text] [PDF]

				Y. Prut and S. I. Perlmutter Firing Properties of Spinal Interneurons during Voluntary Movement. I. State-Dependent Regularity of Firing J. Neurosci., October 22, 2003; 23(29): 9600 - 9610. [Abstract] [Full Text] [PDF]

				M. S. Malmierca, M. A. Merchan, C. K. Henkel, and D. L. Oliver Direct Projections from Cochlear Nuclear Complex to Auditory Thalamus in the Rat J. Neurosci., December 15, 2002; 22(24): 10891 - 10897. [Abstract] [Full Text] [PDF]

				F. E. N. LeBeau, M. S. Malmierca, and A. Rees Iontophoresis In Vivo Demonstrates a Key Role for GABAA and Glycinergic Inhibition in Shaping Frequency Response Areas in the Inferior Colliculus of Guinea Pig J. Neurosci., September 15, 2001; 21(18): 7303 - 7312. [Abstract] [Full Text] [PDF]

				S. Sivaramakrishnan and D. L. Oliver Distinct K Currents Result in Physiologically Distinct Cell Types in the Inferior Colliculus of the Rat J. Neurosci., April 15, 2001; 21(8): 2861 - 2877. [Abstract] [Full Text] [PDF]

				J. Kozloski and J. D. Crawford Transformations of an Auditory Temporal Code in the Medulla of a Sound-Producing Fish J. Neurosci., March 15, 2000; 20(6): 2400 - 2408. [Abstract] [Full Text] [PDF]

				D. A. Bodnar and A. H. Bass Midbrain Combinatorial Code for Temporal and Spectral Information in Concurrent Acoustic Signals J Neurophysiol, February 1, 1999; 81(2): 552 - 563. [Abstract] [Full Text] [PDF]