Structure and function of the moth mushroom body

The mushroom bodies are paired, high-order neuropils in the insect brain involved in complex functions such as learning and memory, sensory integration, context recognition and olfactory processing. This thesis explores the structure of the mushroom bodies in the noctuid moth Spodoptera littoralis using neuroanatomical staining methods, immunocytochemistry and electron microscopy, and investigates how the intrinsic neurons of the mushroom body, the Kenyon cells, respond to olfactory stimulation of the antennae using whole-cell patch clamp technique. The mushroom body in S. littoralis contains about 4,000 Kenyon cells, and consists of a calyx, pedunculus and two lobes, one medial and one vertical. The calyx houses dendritic branches of Kenyon cells and the pedunculus and lobes contain the axons and terminals of these neurons respectively. The calyx is doubled and concentrically divided into a broad peripheral zone, which receives input from antennal lobe projection neurons, and a narrow inner zone, which receives yet unidentified input. The lobes are parsed into three longitudinal divisions, which contain a separate subset of Kenyon cells each. The Kenyon cells are divided into three morphological classes, I-III. Class I Kenyon cells have widely branching spiny dendritic arborisations in both zones of the calyx and occupy the two most posterior subdivisions of the lobes called α/β and α´/β´. Class II Kenyon cells have narrow clawed dendritic trees in the calyx and invade the most anterior division in the lobes, called γ. Class III Kenyon cells have clawed, diffusely branching dendrites in the calyx and provide a separate system of axons and terminal branches, partly detached from the rest of the mushroom body, called the Y tract and lobelets. Kenyon cells within the classes display differential labeling with antisera against neuroactive substances. Kenyon cells make synaptic contact with one another and with other neuron types in the mushroom body. Extrinsic inhibitory and putative modulatory neurons were identified. Whole-cell patch clamp recordings revealed that Kenyon cells exhibit broadly tuned subthreshold activation by odor stimulation and a few cells responded with action potentials to specific biologically relevant odor combinations

On triangular billiards

We prove a conjecture of Kenyon and Smillie concerning the nonexistence of acute rational-angled triangles with the lattice property

Symmetric matrices, Catalan paths, and correlations

Kenyon and Pemantle (2014) gave a formula for the entries of a square matrix in terms of connected principal and almost-principal minors. Each entry is an explicit Laurent polynomial whose terms are the weights of domino tilings of a half Aztec diamond. They conjectured an analogue of this parametrization for symmetric matrices, where the Laurent monomials are indexed by Catalan paths. In this paper we prove the Kenyon-Pemantle conjecture, and apply this to a statistics problem pioneered by Joe (2006). Correlation matrices are represented by an explicit bijection from the cube to the elliptope

Sparse, decorrelated odor coding in the mushroom body enhances learned odor discrimination

Sparse coding may be a general strategy of neural systems for augmenting memory capacity. In Drosophila melanogaster, sparse odor coding by the Kenyon cells of the mushroom body is thought to generate a large number of precisely addressable locations for the storage of odor-specific memories. However, it remains untested how sparse coding relates to behavioral performance. Here we demonstrate that sparseness is controlled by a negative feedback circuit between Kenyon cells and the GABAergic anterior paired lateral (APL) neuron. Systematic activation and blockade of each leg of this feedback circuit showed that Kenyon cells activated APL and APL inhibited Kenyon cells. Disrupting the Kenyon cell–APL feedback loop decreased the sparseness of Kenyon cell odor responses, increased inter-odor correlations and prevented flies from learning to discriminate similar, but not dissimilar, odors. These results suggest that feedback inhibition suppresses Kenyon cell activity to maintain sparse, decorrelated odor coding and thus the odor specificity of memories

Through Trials and Triumph

The Kenyon journey is a collaborative, open-ended and ever-renewing tale of growth, and as a graduating senior, I wrote this letter to the incoming class of 2024, encouraging them to I to take ownership in writing their own Kenyon story while seeking comfort in uncomfortable situations. My senior year has been cut short, but I firmly believe that the Kenyon experience is both the time spent on campus and beyond, as the Kenyon experience is one that is everlasting. This was originally written for the Kenyon Blog, Quintessential Kenyon.https://digital.kenyon.edu/covid19words/1062/thumbnail.jp

Inhibitory muscarinic acetylcholine receptors enhance aversive olfactory conditioning in adult Drosophila

Olfactory associative learning in Drosophila is mediated by synaptic plasticity between the Kenyon cells of the mushroom body and their output neurons. Both Kenyon cells and their inputs from projection neurons are cholinergic, yet little is known about the physiological function of muscarinic acetylcholine receptors in learning in adult flies. Here, we show that aversive olfactory learning in adult flies requires type A muscarinic acetylcholine receptors (mAChR-A), particularly in the gamma subtype of Kenyon cells. mAChR-A inhibits odor responses and is localized in Kenyon cell dendrites. Moreover, mAChR-A knockdown impairs the learning-associated depression of odor responses in a mushroom body output neuron. Our results suggest that mAChR-A function in Kenyon cell dendrites is required for synaptic plasticity between Kenyon cells and their output neurons

Minimizers of Convex Functionals Arising in Random Surfaces

We investigate regularity of minimizers in two dimensions for certain classes of non-smooth convex functionals. In particular our results apply to the surface tensions that appear in recent works on random surfaces and random tilings of Kenyon, Okounkov and othersComment: 32 pages, 1 figur

Localized inhibition in the Drosophila mushroom body

Many neurons show compartmentalized activity, in which activity does not spread readily across the cell, allowing input and output to occur locally. However, the functional implications of compartmentalized activity for the wider neural circuit are often unclear. We addressed this problem in the Drosophila mushroom body, whose principal neurons, Kenyon cells, receive feedback inhibition from a non-spiking interneuron called the anterior paired lateral (APL) neuron. We used local stimulation and volumetric calcium imaging to show that APL inhibits Kenyon cells’ dendrites and axons, and that both activity in APL and APL’s inhibitory effect on Kenyon cells are spatially localized (the latter somewhat less so), allowing APL to differentially inhibit different mushroom body compartments. Applying these results to the Drosophila hemibrain connectome predicts that individual Kenyon cells inhibit themselves via APL more strongly than they inhibit other individual Kenyon cells. These findings reveal how cellular physiology and detailed network anatomy can combine to influence circuit function

Hebbian STDP in mushroom bodies facilitates the synchronous flow of olfactory information in locusts

Odour representations in insects undergo progressive transformations and decorrelatio from the receptor array to the presumed site of odour learning, the mushroom body. There, odours are represented by sparse assemblies of Kenyon cells in a large population. Using intracellular recordings in vivo, we examined transmission and plasticity at the synapse made by Kenyon cells onto downstream targets in locusts. We find that these individual synapses are excitatory and undergo hebbian spike-timing dependent plasticity (STDP) on a ±25 ms timescale. When placed in the context of odour-evoked Kenyon cell activity (a 20-Hz oscillatory population discharge), this form of STDP enhances the synchronization of the Kenyon cells’ targets and thus helps preserve the propagation of the odour-specific codes through the olfactory system

Multiple network properties overcome random connectivity to enable stereotypic sensory responses

Connections between neuronal populations may be genetically hardwired or random. In the insect olfactory system, projection neurons of the antennal lobe connect randomly to Kenyon cells of the mushroom body. Consequently, while the odor responses of the projection neurons are stereotyped across individuals, the responses of the Kenyon cells are variable. Surprisingly, downstream of Kenyon cells, mushroom body output neurons show stereotypy in their responses. We found that the stereotypy is enabled by the convergence of inputs from many Kenyon cells onto an output neuron, and does not require learning. The stereotypy emerges in the total response of the Kenyon cell population using multiple odor-specific features of the projection neuron responses, benefits from the nonlinearity in the transfer function, depends on the convergence:randomness ratio, and is constrained by sparseness. Together, our results reveal the fundamental mechanisms and constraints with which convergence enables stereotypy in sensory responses despite random connectivity