Integrated Calendar

We study the dynamics of dephasing in an ensemble of two level systems undergoing discrete randomizing events with Poisson statistics. A closed form expression for the lineshape is derived in terms of the bare spectrum and the Poisson rate constant. We apply our theory to several interesting cases and obtain surprising results that will be presented in the talk. For Gaussian fluctuations we show deviations from the canonical stochastic theory of Kubo predicting Gumbel like spectra. In realistic 3D harmonic potentials the theory predicts spectra which are significantly different than the Gaussian approximation. Experimental results with optically trapped dense 87Rd atoms will be presented and compared to the theory. Finally, we explain under what circumstances motional narrowing can be transformed into motional broadening.

Classically, the cortex has been studied using electrophysiological techniques, which extract single-cell response profiles with great accuracy but leave other aspects of network responses largely inaccessible. Recently, in vivo two-photon calcium imaging (2PCI), has offered a new “look” into the cortex; allowing the imaging of response profiles and network dynamics from dozens of singly identified neurons simultaneously. I will present our work using both in vivo electrophysiology as well as 2PCI in the primary auditory cortex (A1) of mice highlighting the strengths and weaknesses of both.

We first mapped the functional architecture of A1 in response to pure tones using 2PCI. This new “look” at A1 revealed a surprisingly high level of functional heterogeneity (measured as signal correlation vs. distance) in the face of the known tonotopic organization. The high variance of signal correlations suggested that neurons in A1 are organized in small cortical subnetworks. Additionally, I will discuss our preliminary analysis of population activity (i.e. pairwise noise correlations) and its potential for studying network dynamics in the future.

Next, using in vivo loose patch clamp recordings, we studied the responses to natural sounds in a natural context – the mother-pup bond. We discovered that neuronal activation patterns to pup vocalizations are modulated by pup body odors. Specifically, pup odors significantly enhanced the responsiveness to natural calls of over a third of auditory responsive neurons in lactating females. This plasticity was absent in virgins and decreased in mothers following weaning of their pups. These experiments reveal a previously unknown interaction between natural sounds and smells in the neocortex which is context-dependent and ethologically relevant.