Three-dimensional estimation of the distribution and size of putative functional units in rat gustatory cortex as assessed from the inter-neuronal distance between two neurons with correlative activity

Two neurons recorded simultaneously in rat gustatory cortex often show, whe n the oral mucosa is stimulated with effective taste solutions, correlative activities (CAs), which can be quantified with a cross-correlation techniq ue. It has been suggested that the CAs are involved in taste quality discri mination and the neuron pairs with CA (CA pairs) may function as a unit (pu tative functional unit). The present experiment was undertaken (1) to deter mine the three-dimensional size of putative functional units in rat gustato ry cortex on the basis of the interneuronal distance (IND) in individual CA pairs, and (2) to examine to what extent the CA is related to the intrapai r similarity in taste responses. The findings were as follows: (1) The CAs occurred in 30 out of 55 pairs with INDs less than or equal to 270 mum and often at INDs < 100 mum. (2) The numbers of putative functional units were calculated tentatively by using the longest or the mean INDs; at least 200 or over 4,000 units, respectively. (3) In the CA pairs, the "best taste" wa s identical (homo-type) in many pairs, the "taste profiles" were often simi lar, and the temporal courses of taste responses resembled each other in mo re than one half of the pairs. A possible role of hetero-type pairs was dis cussed. (4) In a small number of cases, troughs were observed in the CCs, s uggesting the involvement of local inhibitory neurons. In conclusion we poi nt out that nearby neurons are prone to CA, if (1) their best tastes are id entical, (2) their taste profiles are similar, and (3) the temporal pattern s of taste response resemble each other. (C) 2001 Elsevier Science Inc.