Fig. 4.

Optimization of the strength of PG inhibition of mitral cells. (A) Activity across a selected 120-glomerulus region of the rat OB in response to the presentation of 2-hexanone. Glomeruli are depicted along the abscissa in arbitrary order; ordinate values represent the activity of selected cell types. Horizontal lines depict baseline activity levels in the absence of odor. (i) Activity profile of OSN inputs (raw glomerular activation). (ii) Resulting activity profiles of ET, SA, and PG cells. (iii) In the absence of PG cell inhibitory input to mitral cells, the activity profile of the mitral cell population (red trace) directly reflects that of the incoming OSNs. The gray trace depicts the calculated z score of OSN activity. (iv) The mitral cell activity profile (red trace) when PG-to-mitral synaptic strength is optimal resembles that of the calculated z score (gray trace). (v) Overly strong inhibition of mitral cells results in broad suppression of mitral cell activity (red trace). (B) Plot of the dissimilarity index (Euclidean distance) between 2-hexanone activity patterns derived from full-scale (2,200-glomerulus) model output and the calculated normalization of the same input data as a function of PG-mitral synaptic weight. Notably, the dissimilarity index is minimal at approximately the same synaptic weight (0.11 arbitrary units) irrespective of stimulus concentration.