ORIGINAL PAPER

Abstract Two distinct neuronal pathways connect the first olfactory neuropil, the antennal lobe, with higher integration areas, such as the mushroom bodies, via antennal lobe projection neurons. Intracellular record-ings were used to address the question whether neu-roanatomical features affect odor-coding properties. We found that neurons in the median antennocerebral tract code odors by latency differences or specific in-hibitory phases in combination with excitatory phases, have a more specific activity profile for different odors and convey the information with a delay. The neurons of the lateral antennocerebral tract code odors by spike rate differences, have a broader activity profile for different odors, and convey the information quickly. Thus, rather preliminary information about the olfac-tory stimulus first reaches the mushroom bodies and the lateral horn via neurons of the lateral antennoce-rebral tract and subsequently odor information be-comes more specified by activities of neurons of the median antennocerebral tract. We conclude that this neuroanatomical feature is not related to the distinction between different odors, but rather reflects a dual coding of the same odor stimuli by two different neu-ronal strategies focusing different properties of the same stimulus