Randolf Menzel

Department of Neurobiology

Freie Universität Berlin, Germany

http://www.neurobiologie.fu-berlin.de/menzel/menzel.html

Friday, October 9

12-1:30pm

Watching a small but intelligent brain as it learns and remembers

Honeybees have small brains, but their behavioural repertoire is

impressive. They navigate over several kilometers using a geometric

reference system of the environment. They communicate about important

places by a ritualized movement (the waggle dance) indicating distance

and direction to the particular location from their nest site. They

learn about the features of food sources (color, odor, shape, relative

position). Reward learning in honeybees initiates a sequence of neural

processes that lead to long-lasting memory, and pass through multiple

transient memory phases. The lecture will present our top down strategy

starting with behavioral observations under nature conditions,

establishing a reduced but whole animal preparation that reflects the

essential properties of associative learning and allows for the study of

associative learning at the behavioral and neural level.

Opto- and electrophysiological recordings are applied to study

associative plasticity at the level of the single neuron and neural

circuits in an animal that still shows behavioral learning, memory

formation and retrieval. The report shall focus on recent data collected

from the mushroom body, a high order integration center of the insect

brain. Imaging of the input region of the mushroom bodies reveals that

odors are represented in specific patterns of pre- and postsynaptic

activations. A comparison of the dynamics of the odor responses shows

that mushroom body intrinsic neurons (Kenyon cells) code odors in a

sparse way both in the time domain and on the population level. Odor

learning leads to changes of the synaptic transmission at the input

synapses to these Kenyon cells to both the trained and specifically not

trained odor.

The optophysiological approach allows us to trace memory not only with

respect to the mechanisms involved in forming the memory but also to the

patterns of synaptic plasticity that store the contents of the memory.

Single neuron intracellular and extracellular recordings as well as

multi-unit recordings of mushroom body output neurons reveal a recoding

strategy of the mushroom body from a stimulus space to a value space. A

model will be presented that captures the results of our recordings, and

assigns particular functions to the input and output side of the

mushroom body in the bee brain.

Neuroscience in general needs model systems to unravel the intricate and

complex working of the brain. Insects provide us with the ideal

situation to address basic problems of brain science at a level of

neural complexity that can be analyzed with the available methods using

animals that still are able to behave. I shall highlight the unique

opportunities of insects in the search for the neural basis of learning

and memory.