Encoding a temporally structured stimulus with a temporally structured neural representation

Abstract

Sensory neural systems use spatiotemporal coding mechanisms to represent stimuli. These time-varying response patterns sometimes outlast the stimulus. Can the temporal structure of a stimulus interfere with, or even disrupt, the spatiotemporal structure of the neural representation? We investigated this potential confound in the locust olfactory system. When odors were presented in trains of nearly overlapping pulses, responses of first-order interneurons (projection neurons) changed reliably, and often markedly, with pulse position as responses to one pulse interfered with subsequent responses. However, using the responses of an ensemble of projection neurons, we could accurately classify the odorants as well as characterize the temporal properties of the stimulus. Further, we found that second-order follower neurons showed firing patterns consistent with the information in the projection-neuron ensemble. Thus, ensemble-based spatiotemporal coding could disambiguate complex and potentially confounding temporally structured sensory stimuli and thereby provide an invariant response to a stimulus presented in various ways.

Odor representations in the olfactory bulb evolve after the first breath and persist as an odor afterimage

“…Some forms of olfactory dynamics have been observed before. In invertebrates, odors elicit complex temporal patterns (43,44) that stabilize over time (10,11). In contrast to the gradual changes observed in invertebrates, we observed an abrupt change in the representation between the first and second breath.…”

“…These dynamics can persist even after the cessation of stimulus, which can take the form of an off-response or prolonged aftereffect. Aftereffects have been intensely studied in vision (1,3) and also observed in audition (4,5), touch (6,7), taste (here the afterimages may be due to persistent ligand binding) (8,9), and insect olfaction (10,11). In mammalian olfaction, the only reported aftereffect is a "persistent afterdischarge" following high concentration odors (12).…”

Dopaminergic Modulation of the Striatal Microcircuit: Receptor-Specific Configuration of Cell Assemblies

“…To identify neuronal pools firing in synchrony, we constructed temporal neuronal population vectors out of the synchrony peaks (see above). Each vector represents the activation of different neurons within a time window (Brown et al, 2005;Sasaki et al, 2007;Carrillo-Reid et al, 2008). To set significance levels for the appearance of these vectors, we generated 1000 shuffled raster plots from each experimental condition and compared the random distribution against the real data (Mao et al, 2001;Cossart et al, 2003;Carrillo-Reid et al, 2008).…”

“…Only synchrony peaks with more cells than those expected by chance (p Ͻ 0.01) were considered for additional analysis. Together, the sequence of synchrony peaks (neuronal population vectors) represent the overall activity of the microcircuit along time, that is, the sequence of network states making up the dynamics (Schreiber et al, 2003;Stopfer et al, 2003;Brown et al, 2005;Sasaki et al, 2007;Carrillo-Reid et al, 2008). To know whether synchronization increased after a given treatment, the number of synchrony peaks (population vectors) was counted in each of several 3 min epochs (image sequences) at different times in the same experiment and averaged.…”

Techniques for extracting single-trial activity patterns from large-scale neural recordings

“…An example from the sensory domain is illustrated in figure 3A. Presentation of an odor initiates an evolving pattern of neural activity that outlasts the stimulus, and takes time to return to its starting state [53, also see 54,55,56]. In that study, not all neurons were recorded simultaneously, and some trial-averaging was performed to combat noise (each trajectory averages three trials).…”