Piriform cortex functional heterogeneity revealed by cellular responses to odours

Abstract

The role of the piriform cortex (PC) in olfactory information processing remains mainly unknown. Indeed, until recently, only a few studies have investigated the response of PC neurons to odours and these studies did not take into account the functional heterogeneity of the PC previously described using an electrical stimulation paradigm. In this experiment, extracellular activity in response to odour was recorded in urethane anaesthetized rats in the different parts of the cortex ranging from anterior to posterior. A large percentage of cortical cells were silent at rest, and this percentage increased from anterior to posterior. Analysis of odour evoked activity revealed a large percentage of nonresponsive cells that increased from anterior to posterior. Cell activity was largely synchronized with breathing and different temporal patterns were observed. The anterior PC was characterized by odour-evoked responses phase-locked with the inhalation-exhalation transition period. By contrast, activity in the posterior PC was mainly phase-locked with inhalation or exhalation. These data confirm the spatial functional heterogeneity previously reported in the PC. Functional anatomy of the PC suggests that activity in the anterior PC can be mainly driven by afferent activity coming from the OB whereas posterior cells were certainly entrained by more complex mechanisms.

RETRACTED: Odor maps in the olfactory cortex

“…One possible explanation for this difference is that c-Fos is not detected in neurons that are only weakly activated by an odorant. However, electrophysiological recordings similarly indicate that single odorants activate only a small percentage of neurons in the piriform cortex (32,33,35,36,38), arguing against this possibility. Another potential explanation for the observed difference between OR inputs and neuronal activation is that intrinsic inhibitory circuits shape odor responses in the cortex and eliminate responses to a particular odorant by many neurons that receive input from a given OR.…”

“…At the other extreme, signals from the different ORs might be targeted to many different locations, resulting in a highly distributed odor code. Previous electrophysiological studies (32)(33)(34)(35)(36)(37)(38) have described odorant responses by individual OC neurons but have not examined the spatial patterning of OC odor responses.…”

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

“…In addition to temporal patterns in odorant-evoked activity, phasic activity related to the respiratory cycle was prominent in most single units as has been reported previously (Wilson, 1998;Litaudon et al, 2003). The most direct explanation for this respiration-locked activity is a reflection of similar activity in the cortical afferent, mitral/tufted cells Chaput et al, 1992).…”

Diverse Patterns of Odor Representation by Neurons in the Anterior Piriform Cortex of Awake Mice

“…At ϳ300 ms after the opening of final solenoid valve, vigorous firing of action potentials were evoked during the entire period of odorant application (2 s). The spike firing was rhythmic at 4 -5 Hz, suggesting activity coupled to respiratory cycles (Wilson, 1998;Litaudon et al, 2003;Rennaker et al, 2007). Moreover, the responses were reliable across multiple consecutive trials when the same odorant was presented (Fig.…”