Neural Correlates of Odor Learning in the Presynaptic Microglomerular Circuitry in the Honeybee Mushroom Body Calyx.
News from Jun 12, 2018
Calcium imaging, Honeybee, Learning and Memory, Mushroom body, Projection neurons
The mushroom body (MB) in insects is known as a major center for associative learning and memory, though exact locations for the correlating memory traces remain to be elucidated. Here we asked whether presynaptic boutons of olfactory projection neurons in the main input site of the MB undergo neuronal plasticity during classical odor-reward conditioning and correlate with the conditioned behavior. We simultaneously measured Ca2+ responses in the boutons and conditioned behavioral responses to learned odors in honeybees. We found that the absolute amount of the neural change for the rewarded but not for the unrewarded odor was correlated with the behavioral learning rate across individuals. The temporal profile of the induced changes matched with odor response dynamics of the MB-associated inhibitory neurons, suggestive of activity modulation of boutons by this neural class. We hypothesize the circuit-specific neural plasticity relates to the learned value of the stimulus and underlies the conditioned behavior of the bees.
In order to understand memory processing in the brain, it is important to identify the synaptic locations and activities where memory information is stored. This requires monitoring neuronal activity in behaving animals, a technically very demanding task especially in tiny insects. Here we succeeded to measure neuronal activity from restrained yet behaving honeybees. We recorded the activity of olfactory projection neurons from the mushroom body, an insect brain center for learning and memory, while bees are performing an olfactory reward learning task. We found that the amount of neural plasticity correlates with the quantitative expression of a learned behavior to the sugar rewarded odor. Our results contribute to the understanding of the physiologic basis of memory formation in an insect brain.
eNeuro 11 June 2018, ENEURO.0128-18.2018. Link