Sensory memory for odors is encoded in spontaneous correlated activity between olfactory glomeruli

Sensory memory is a short-lived persistence of a sensory stimulus in the nervous system, such as iconic memory in the visual system. However, little is known about the mechanisms underlying olfactory sensory memory. We have therefore analyzed the effect of odor stimuli on the first odor-processing network in the honeybee brain, the antennal lobe, which corresponds to the vertebrate olfactory bulb. We stained output neurons with a calcium-sensitive dye and measured across-glomerular patterns of spontaneous activity before and after a stimulus. Such a single-odor presentation changed the relative timing of spontaneous activity across glomeruli in accordance with Hebb's theory of learning. Moreover, during the first few minutes after odor presentation, correlations between the spontaneous activity fluctuations suffice to reconstruct the stimulus. As spontaneous activity is ubiquitous in the brain, modifiable fluctuations could provide an ideal substrate for Hebbian reverberations and sensory memory in other neural systems

Investigations of changes of the neuronal representation of odors caused by associative and non associative learning in the antennal lobe of the honey bee, Apis mellifera

1\. Titelblatt und Inhaltsverzeichnis 2\. Einleitung 3\. Material und Methoden 4\. Ergebnisse 5\. Diskussion 6\. LiteraturIn dieser Arbeit wurde mit Hilfe eines kalziumsensitiven Farbstoffes (FURA) an Bienen die Aktivität der Ausgangsneurone des Antennallobus, den Projektionsneuronen, in drei verschiedenen Versuchssituationen gemessen. Im Sensitisierungsexperiment wurde untersucht, wie ein mögliches neuronales Korrelat für die im Verhalten gefundenen Reaktionen aussehen könnte. Es konnte gezeigt werden, dass sensitisierte Bienen bis zu 6,5 Minuten eine höhere duftinduzierte Kalziumkonzentration in Projektionsneuronen des wichtigsten Glomerulus für ein Duftmuster aufweisen als nicht sensitisierte Tiere. Die Ergebnisse lassen vermuten, dass zumindest für den ersten Messpunkt 30 Sekunden nach der Sensitisierung die erhöhte Kalziumkonzentration in den Projektionsneuronen eine Verhaltensreaktion (PER) nach sich zieht. Im zweiten Experiment wurde untersucht, ob und wie eine Duftpräsentation die stetig vorhandenen spontanen Kalziumfluktuationen in den Projektionsneuronen verändert. Die Spontanaktivitätsexperimente zeigten, dass eine Duftstimulation die Korrelation zwischen Glomeruli im Mittel senkt. Die Korrelation zwischen Duftglomeruli steigt jedoch. Dieses Ergebnis lässt darauf schließen, dass Spuren des Duftes nach dessen Wahrnehmung im Netzwerk "AL" in Form einer erhöhten Korrelation zwischen Duftglomeruli vorhanden sind. Die Verhaltensexperimente wurden durchgeführt, um zu untersuchen, wie Veränderungen im Verhalten neuronal repräsentiert sind. Es konnte gezeigt werden, dass die duftinduzierte Erhöhung der Kalziumkonzentration in den Projektionsneuronen 5 Minuten nach einer differentiellen Konditionierung für den CS+ und die Kontrolldüfte verstärkt ist, nicht aber für den CS-. Bei Tieren, die 15 Minuten nach dem Training getestet wurden, wurde dieser Effekt nicht gefunden. Es kann somit vermutet werden, dass für eine Verhaltensreaktion eine erhöhte duftinduzierte Kalziumkonzentration in den Projektionsneuronen nur 5 Minuten nach dem Training nötig ist.In this work the activity of the output neurons of the antennal lobe (projection neurons) of the honeybee was measured under three different conditions, using a calcium-sensitive dye (FURA). The first experiment investigated a possible neuronal correlate for behaviour following sensitization. It appeared that up to 6.5 minutes after sensitization sensitized bees showed a higher odor-evoked calcium concentration in projection neurons of the most sensitive glomerulus of a given odor pattern than non-sensitized bees. The results suggest that at least for the first measuring point after sensitization (30s) an increased calcium concentration in the projection neurons is required for a behaviour response (PER). The second experiment tested whether and how an odor presentation changes ongoing spontaneous calcium fluctuations in the projection neurons. It was shown that mean correlation between glomeruli decreases after odor presentation. Correlation increases between those glomeruli that are most sensitive to a given odor. The results presume that after being perceived the odor leaves traces in the network "AL" in form of an increased correlation between glomeruli most sensitive to this odor. The last experiments were done to investigate how changes in behavior are represented neuronaly. It could be shown that 5 minutes after a differential conditioning the calcium concentration in the projection neurons is increased for the CS+ and the control odors, but not for the CS-. Animals tested 15 minutes after differential conditioning did not show this effect. Therefore it can be presumed that an increased odor-induced calcium concentration in the projection neurons is necessary for a behavior response only 5 minutes after training

Sensory Memory for Odors is Encoded in Spontaneous Correlated Activity between

Sensory memory is a short-lived persistence of a sensory stimulus in the nervous system, such as iconic memory in the visual system. However, little is known about the mechanisms underlying olfactory sensory memory. We have therefore analyzed the effect of odor stimuli on the first odor-processing network in the honeybee brain, the antennal lobe, which corresponds to the vertebrate olfactory bulb. We stained output neurons with a calcium sensitive dye, and measured across-glomerular patterns of spontaneous activity before and after a stimulus. Such a single odor presentation changed the relative timing of spontaneous activity across glomeruli in accordance with Hebb’s theory of learning. Moreover, during the first few minutes after odor presentation, correlations between the spontaneous activity fluctuations suffice to reconstruct the stimulus. As spontaneous activity is ubiquitous in the brain, modifiable fluctuations could provide an ideal substrate for Hebbian reverberations and sensory memory in other neural systems