The Effect of Correlated Neuronal Firing and Neuronal Heterogeneity on Population Coding Accuracy in Guinea Pig Inferior Colliculus

In the auditory system, some ascending pathways preserve the precise timing information present in a temporal code of frequency. This can be measured by studying responses that are phase-locked to the stimulus waveform. At each stage along a pathway, there is a reduction in the upper frequency limit of the phase-locking and an increase in the steady-state latency. In the guinea pig, phase-locked responses to pure tones have been described at various levels from auditory nerve to neocortex but not in the inferior colliculus (IC). Therefore we made recordings from 161 single units in guinea pig IC. Of these single units, 68% (110/161) showed phase-locked responses. Cells that phase-locked were mainly located in the central nucleus but also occurred in the dorsal cortex and external nucleus. The upper limiting frequency of phase-locking varied greatly between units (80−1,034 Hz) and between anatomical divisions. The upper limits in the three divisions were central nucleus, >1,000 Hz; dorsal cortex, 700 Hz; external nucleus, 320 Hz. The mean latencies also varied and were central nucleus, 8.2 ± 2.8 (SD) ms; dorsal cortex, 17.2 ms; external nucleus, 13.3 ms. We conclude that many cells in the central nucleus receive direct inputs from the brain stem, whereas cells in the external and dorsal divisions receive input from other structures that may include the forebrain.

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Effects of Cochlear Trauma on BDNF Expression in Guinea Pig Cochlear Nucleus and Inferior Colliculus

otolaryngology ◽

10.4172/2161-119x.s3-006 ◽

2013 ◽

Author(s):

Rodger J Albertsen M

Keyword(s):

Guinea Pig ◽

Inferior Colliculus ◽

Cochlear Nucleus ◽

Bdnf Expression

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Responses in the Inferior Colliculus of the Guinea Pig to Concurrent Harmonic Series and the Effect of Inactivation of Descending Controls

Journal of Neurophysiology ◽

10.1152/jn.00451.2009 ◽

2010 ◽

Vol 103 (4) ◽

pp. 2050-2061 ◽

Cited By ~ 21

Author(s):

Kyle T. Nakamoto ◽

Trevor M. Shackleton ◽

Alan R. Palmer

Keyword(s):

Guinea Pig ◽

Auditory Cortex ◽

Inferior Colliculus ◽

Sound Level ◽

Harmonic Series ◽

Natural Environments ◽

Multiple Sources ◽

Spike Response ◽

Relative Level ◽

Communication Calls

One of the fundamental questions of auditory research is how sounds are segregated because, in natural environments, multiple sounds tend to occur at the same time. Concurrent sounds, such as two talkers, physically add together and arrive at the ear as a single input sound wave. The auditory system easily segregates this input into a coherent percept of each of the multiple sources. A common feature of speech and communication calls is their harmonic structure and in this report we used two harmonic complexes to study the role of the corticofugal pathway in the processing of concurrent sounds. We demonstrate that, in the inferior colliculus (IC) of the anesthetized guinea pig, deactivation of the auditory cortex altered the temporal and/or the spike response to the concurrent, monaural harmonic complexes. More specifically, deactivating the auditory cortex altered the representation of the relative level of the complexes. This suggests that the auditory cortex modulates the representation of the level of two harmonic complexes in the IC. Since sound level is a cue used in the segregation of auditory input, the corticofugal pathway may play a role in this segregation.

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Low-Voltage Activated T-Type Calcium Currents Are Differently Expressed in Superficial and Deep Layers of Guinea PigPiriform Cortex

Journal of Neurophysiology ◽

10.1152/jn.1998.79.2.808 ◽

1998 ◽

Vol 79 (2) ◽

pp. 808-816 ◽

Cited By ~ 16

Author(s):

Jacopo Magistretti ◽

Marco de Curtis

Keyword(s):

Guinea Pig ◽

Calcium Current ◽

Low Voltage ◽

Piriform Cortex ◽

Neuronal Firing ◽

Calcium Currents ◽

Patch Clamp Technique ◽

Voltage Range ◽

Deep Layers ◽

Group 2

Magistretti, Jacopo and Marco de Curtis. Low-voltage activated T-type calcium currents are differently expressed in superficial and deep layers of guinea pig piriform cortex. J. Neurophysiol. 79: 808–816, 1998. A variety of voltage-dependent calcium conductances are known to control neuronal excitability by boosting peripheral synaptic potentials and by shaping neuronal firing patterns. The existence and functional significance of a differential expression of low- and high-voltage activated (LVA and HVA, respectively) calcium currents in subpopulations of neurons, acutely isolated from different layers of the guinea pig piriform cortex, were investigated with the whole cell variant of the patch-clamp technique. Calcium currents were recorded from pyramidal and multipolar neurons dissociated from layers II, III, and IV. Average membrane capacitance was larger in layer IV cells [13.1 ± 6.2 (SD) pF] than in neurons from layers II and III (8.6 ± 2.8 and 7.9 ± 3.1 pF, respectively). Neurons from all layers showed HVA calcium currents with an activation voltage range positive to −40 mV. Neurons dissociated from layers III and IV showed an LVA calcium current with the biophysical properties of a T-type conductance. Such a current displayed the following characteristics: 1) showed maximal amplitude of 11–16 pA/pF at −30 mV, 2) inactivated rapidly with a time constant of ∼22 ms at −30 mV, and 3) was completely steady-state inactivated at −60 mV. Only a subpopulation of layer II neurons (group 2 cells; circa 18%) displayed an LVA calcium current similar to that observed in deep layers. The general properties of layer II-group 2 cells were otherwise identical to those of group 1 neurons. The present study demonstrates that LVA calcium currents are differentially expressed in neurons acutely dissociated from distinct layers of the guinea pig piriform cortex.

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Optimal Short-Term Population Coding: When Fisher Information Fails

Neural Computation ◽

10.1162/08997660260293247 ◽

2002 ◽

Vol 14 (10) ◽

pp. 2317-2351 ◽

Cited By ~ 66

Author(s):

M. Bethge ◽

D. Rotermund ◽

K. Pawelzik

Keyword(s):

Fisher Information ◽

Dynamic Range ◽

Mean Squared Error ◽

Average Rate ◽

Neuronal Response ◽

Minimum Mean Square Error ◽

Population Coding ◽

Neuronal Firing ◽

Tuning Curves ◽

Efficient Coding

Efficient coding has been proposed as a first principle explaining neuronal response properties in the central nervous system. The shape of optimal codes, however, strongly depends on the natural limitations of the particular physical system. Here we investigate how optimal neuronal encoding strategies are influenced by the finite number of neurons N (place constraint), the limited decoding time window length T (time constraint), the maximum neuronal firing rate fmax (power constraint), and the maximal average rate fmax (energy constraint). While Fisher information provides a general lower bound for the mean squared error of unbiased signal reconstruction, its use to characterize the coding precision is limited. Analyzing simple examples, we illustrate some typical pitfalls and thereby show that Fisher information provides a valid measure for the precision of a code only if the dynamic range (fmin T, fmax T) is sufficiently large. In particular, we demonstrate that the optimal width of gaussian tuning curves depends on the available decoding time T. Within the broader class of unimodal tuning functions, it turns out that the shape of a Fisher-optimal coding scheme is not unique. We solve this ambiguity by taking the minimum mean square error into account, which leads to flat tuning curves. The tuning width, however, remains to be determined by energy constraints rather than by the principle of efficient coding.

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Regularity of Firing of Neurons in the Inferior Colliculus

Journal of Neurophysiology ◽

10.1152/jn.1997.77.6.2945 ◽

1997 ◽

Vol 77 (6) ◽

pp. 2945-2965 ◽

Cited By ~ 63

Author(s):

Adrian Rees ◽

Ali Sarbaz ◽

Manuel S. Malmierca ◽

Fiona E. N. Le Beau

Keyword(s):

Guinea Pig ◽

Characteristic Feature ◽

Firing Rate ◽

Inferior Colliculus ◽

Coefficient Of Variation ◽

Stimulus Level ◽

The Other ◽

Central Nucleus ◽

Spike Discharge ◽

Primary Type

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 (Cs), chop-onset (Co)]; pausers [42%: pauser-chop-sustained(P/Cs), pauser-chop-onset (P/Co), 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: Cs and P/Cs units were highly regular throughout their response, whereas Co and P/Co 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 (Cs, Co, P/Cs, and P/Co). Other PSTH types may or may not exhibit regularity.

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