Patterned response to odor in mammalian olfactory bulb: the influence of intensity

Abstract

Responses of single neurons in the olfactory bulb of anesthetized hamsters were recorded extracellularly while odors of defined concentration and time course were delivered to the olfactory system at constant flow. Responses could be either excitatory or suppressive, as judged by the first distinguishable change in firing rate during odor delivery. However, when the time course of the response was examined in more detail, approximately one-third of all tests and one-half of the tests at high concentration resulted in complex temporal patterns of firing rate that involved both increases and decreases with respect to spontaneous activity. Approximately two-thirds of all tests produced responses where increased firing rate preceded any distinguishable suppression. Excitatory and suppressive responses were each classified into four groups according to their temporal patterns. Different patterns were not equally represented in the data and the proportions of patterns elicited by the same odor changed with stimulus intensity. Complex responses, where temporal patterns included periods of firing rate above and below spontaneous rate, were increasingly common and intensity was increased. Magnitude of response is difficult to define when a single response includes both increases and decreases of firing rate but more than half of the neurons that responded to more than one stimulus concentration clearly had nonmonotonic intensity-response functions. Forty-one out of 101 neurons were classified as output cells because they could be driven at short constant latency by lateral olfactory tract stimulation. Their responses were not clearly different from the remaining cells that could not be classified as output cells. The contribution of the inhibitory circuits of the olfactory bulb to the generation of patterned response and to changes in pattern with intensity are discussed. The lateral inhibitory circuits of the bulb appear to be sufficient to explain the data presented here.

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

“…An excitatory persistent afterdischarge that lasts for tens of seconds has previously been reported in the M/T cells of anesthetized mice following odor presentation at 25-50% dilution (12), and short off-responses have been observed in frogs and hamsters (29,57). In comparison, we observe varied postodor responses including phase changes and inhibition, and our olfactory afterimage lasts only a few seconds.…”

“…Seeing that the concentration could change 5-10% between the first and second breath, we were concerned that the representation change between these breaths was due to concentration and not neural dynamics, as these changes are near the intensity discrimination threshold for rats (26). Previous investigations into concentration coding in olfaction have looked at changes in concentration of orders of magnitude, not a few percent (27)(28)(29). Given that the concentration changes over the time range of the first breath, we used the variability in breathing as a proxy for small changes in odor concentration ( Fig.…”

Adaptation of the odour‐induced response in frog olfactory receptor cells

“…Furthermore, some features of the patterns of spike firing exhibited by olfactory receptors appear to be preserved in the mitral and tufted cells within the olfactory bulb. The increase in spike firing frequency, the reduction in the number of spikes fired and the reduction in latency to the first spike evoked from an isolated olfactory receptor by increasing odour concentration closely resemble the excitatory responses of mitral and tufted cells (Doeving, 1964;Kauer, 1974;Kauer & Shephard, 1977;Harrison & Scott, 1986;Meredith, 1986). Intriguingly, similar response properties have also been observed for individual cells within the olfactory cortex (Duchamp-Viret et al 1996).…”

Spatial and Temporal Distribution of Odorant-Evoked Activity in the Piriform Cortex

“…Most naturally occurring odors are complex mixtures, and the spatial pattern of glomerular activity reflects both individual components (Lin et al, 2006) and early intercomponent interactions (Joerges et al, 1997;Vickers et al, 1998;Tabor et al, 2004). In addition to spatial patterns, both glomerular (Spors et al, 2006) and mitral/ tufted cell activity (Meredith, 1986;Cang and Isaacson, 2003) demonstrate stimulus-specific temporal structure.…”