BIS236 Neural Circuits: Olfactory Learning and Memory Flashcards

Flashcards covering the vocabulary and concepts of olfactory learning, neural circuitry in Drosophila, and comparative neuroanatomy from the BIS236 lecture.

Kenyon cells ($KC$)

Third-order neurons (~$2000$) in the Drosophila olfactory system that receive input from projection neurons and fire very selectively.

Projection neurons ($PN$)

Second-order neurons (~$150$) that relay olfactory information from receptor neurons to Kenyon cells.

Sparse selective code

The result of Kenyon cells requiring multiple simultaneous inputs to fire, turning a dense combinatorial code into one where only a small fraction of cells respond.

GAL4/UAS system

A genetic tool allowing the artificial expression of arbitrary transgenes in specific cells using a yeast transcription factor (GAL4) and an Upstream Activating Sequence (UAS).

Split-GAL4 system

A technique providing higher specificity by splitting GAL4 into a DNA Binding Domain ($DBD$) and an Activation Domain ($AD$), which only drive expression where both are present.

Calyx

The region of the mushroom body where the dendrites of Kenyon cells are located.

Peduncle

The bundle of Kenyon cell axons that passes through the brain before branching into horizontal and vertical lobes.

MBON (Mushroom Body Output Neuron)

Neurons that receive input from Kenyon cell axons in specific compartments and mediate behavioral outputs like approach or avoidance.

DAN (Dopaminergic Neuron)

Neurons that innervate specific compartments of the mushroom body and provide reward or punishment signals to entrain memory.

Valence

The intrinsic 'goodness' (appetitive) or 'badness' (aversive) associated with a stimulus or the behavior it triggers.

Classical conditioning

A learning process where a Conditioned Stimulus ($CS$) is paired with an Unconditioned Stimulus ($US$) so the animal can predict future events.

Synaptic depression

The weakening of connections, specifically between Kenyon cells and MBONs, which underlies olfactory memory in Drosophila.

Optogenetics

The use of light-sensitive proteins, such as channelrhodopsin, to activate specific neurons (e.g., DANs or MBONs) artificially using LED light.

Paired-pulse ratio

An electrophysiological measure used to indicate pre-synaptic release probability by stimulating a neuron twice in quick succession.

Paired-pulse depression

A phenomenon where the second postsynaptic pulse is smaller because the pre-synaptic neuron depleted its vesicles, indicating a high release probability.

Paired-pulse facilitation

A phenomenon where the second postsynaptic pulse is larger due to leftover $Ca^{2+}$ in the pre-synaptic terminal, indicating a low release probability.

Cerebellum

A vertebrate brain structure that mediates motor learning and error correction, considered a conserved analog to the insect mushroom body.

Mossy fibers

In the cerebellum, these are the input fibers analogous to olfactory projection neurons in the fly mushroom body.

Granule cells

Cerebellar neurons that are the functional equivalent of Kenyon cells in the insect mushroom body.

Purkinje cells

The output neurons of the cerebellum, analogous to the Mushroom Body Output Neurons ($MBONs$) in flies.

Climbing fibers

In the cerebellum, these fibers provide instruction or error signals, similar to the roles of Dopaminergic Neurons ($DANs$) in the fly.

Electrosensory lobe

A cerebellum-like structure in weakly electric fish that allows the animal to learn to ignore its own electric organ signals.

Evaluator

The functional role of dopaminergic neurons in the learning loop, determining if sensory input is positive (food) or negative (shocks).

Inward current

A flow of ions into a neuron recorded during patch-clamp electrophysiology, represented by a downward deflection in traces.

DNA Binding Domain ($DBD$)

The half of the split-GAL4 protein that binds to the UAS sequence.