For more details on how we estimated information in neural responses, see
I. Nelken, G. Chechik, T.D. Mrsic Flogel A.J. King and J.W.H. Schupp
Encoding stimulus information by spike numbers and mean response time in primary auditory cortex. J. Computational Neuroscience 19(2):199-221, (2005)
Neurons can transmit information about sensory stimuli via their firing rate, spike latency, or by the occurrence of complex spike patterns. Identifying which aspects of the neural responses actually encode sensory information remains a fundamental question in neuroscience. Here we compared various approaches for estimating the information transmitted by neurons in auditory cortex in two very different experimental paradigms, one measuring spatial tuning and the other responses to complex natural stimuli. We demonstrate that, in both cases, spike counts and mean response times jointly carry essentially all the available information about the stimuli. Thus, in auditory cortex, whereas spike counts carry only partial information about stimulus identity or location, the additional availability of relatively coarse temporal information is sufficient in order to extract essentially all the sensory information available in the spike discharge pattern, at least for the relatively short stimuli (< 100 ms) commonly used in auditory research.

For a discussion of the paper, see
Jan Schnupp
Auditory Filters, Features, and Redundant Representations.
Neuron, Vol 51, 278-280, (2006)

Responses in auditory cortex tend to be weaker, more phasic, and noisier than those of auditory brainstem and midbrain nuclei. Is the activity in cortex therefore merely a "degraded echo" of lower-level neural representations? In this issue of Neuron, Chechik and colleagues show that, while cortical responses indeed convey less sensory information than auditory midbrain neurons, their responses are also much less redundant.

For more details on the auditory responses to the same stimuli, see
Omer Bar-Yosef, Yaron Rotman and Israel Nelken
Responses of neurons in cat primary auditory cortex to bird chirps: effects of temporal and spectral context. J. Neurosci. 22, 8619-8632 (2002)
The responses of neurons to natural sounds and simplified natural sounds were recorded in the primary auditory cortex (AI) of halothane-anesthetized cats. Bird chirps were used as the base natural stimuli. They were first presented within the original acoustic context (at least 250 msec of sounds before and after each chirp). The first simplification step consisted of extracting a short segment containing just the chirp from the longer segment. For the second step, the chirp was cleaned of its accompanying background noise. Finally, each chirp was replaced by an artificial version that had approximately the same frequency trajectory but with constant amplitude. Neurons had a wide range of different response patterns to these stimuli, and many neurons had late response components in addition, or instead of, their onset responses. In general, every simplification step had a substantial influence on the responses. Neither the extracted chirp nor the clean chirp evoked a similar response to the chirp presented within its acoustic context. The extracted chirp evoked different responses than its clean version. The artificial chirps evoked stronger responses with a shorter latency than the corresponding clean chirp because of envelope differences. These results illustrate the sensitivity of neurons in AI to small perturbations of their acoustic input. In particular, they pose a challenge to models based on linear summation of energy within a spectrotemporal receptive field.