@article {64825, title = {Neural basis for looming size and velocity encoding in the Drosophila giant fiber escape pathway.}, journal = {Current Biology : CB}, volume = {29}, year = {2019}, month = {2019 Feb 28}, pages = {1073}, abstract = {

Identified neuron classes in vertebrate cortical [1-4] and subcortical [5-8] areas and invertebrate peripheral [9-11] and central [12-14] brain neuropils encode specific visual features of a panorama. How downstream neurons integrate these features to control vital behaviors, like escape, is unclear [15]. In Drosophila, the timing of a single spike in the giant fiber (GF) descending neuron [16-18] determines whether a fly uses a short or long takeoff when escaping a looming predator [13]. We previously proposed that GF spike timing results from summation of two visual features whose detection is highly conserved across animals [19]: an object{\textquoteright}s subtended angular size and its angular velocity [5-8, 11, 20, 21]. We attributed velocity encoding to input from lobula columnar type 4 (LC4) visual projection neurons, but the size-encoding\ source remained unknown. Here, we show that lobula plate/lobula columnar, type 2 (LPLC2) visual projection neurons anatomically specialized to detect looming [22] provide the entire GF size component. We find LPLC2 neurons to be necessary for GF-mediated escape and show that LPLC2 and LC4 synapse directly onto the GF via reconstruction in a fly brain electron microscopy (EM) volume [23]. LPLC2 silencing eliminates the size component of the GF looming response in patch-clamp recordings, leaving only the velocity component. A model summing a linear function of angular velocity (provided by LC4) and a Gaussian function of angular size (provided by LPLC2) replicates GF looming response dynamics and predicts the peak response time. We thus present an identified circuit in which information from looming feature-detecting neurons is combined by a common post-synaptic target to determine behavioral output.

}, issn = {1879-0445}, doi = {10.1016/j.cub.2019.01.079}, author = {Ache, Jan M and Polsky, Jason and Alghailani, Shada and Parekh, Ruchi and Breads, Patrick and Peek, Martin Y and Bock, Davi D and von Reyn, Catherine R and Card, Gwyneth M} } @article {48600, title = {Feature integration drives probabilistic behavior in the Drosophila escape response.}, journal = {Neuron}, volume = {94}, year = {2017}, month = {2017 Jun 21}, pages = {1190-204}, abstract = {

Animals rely on dedicated sensory circuits to extract and encode environmental features. How individual neurons integrate and translate these features into behavioral responses remains a major question. Here, we identify a visual\ projection neuron\ type that conveys predator approach information to the\ Drosophila\ giant fiber (GF) escape circuit. Genetic removal of this input during looming stimuli reveals that it encodes angular expansion velocity, whereas other input cell type(s) encode angular size. Motor program selection and timing emerge from\ linear\ integration of these two features within the GF. Linear integration improves size detection invariance over prior models and appropriately biases motor selection to rapid,\ GF-mediated\ escapes during fast looms. Our findings suggest\ feature integration, and motor control may occur as simultaneous operations within the same neuron and establish the\ Drosophila\ escape circuit as a model system in which these computations may be further dissected at the circuit level.

}, doi = {10.1016/j.neuron.2017.05.036}, author = {von Reyn, Catherine R and Nern, Aljoscha and Williamson, W Ryan and Breads, Patrick and Wu, Ming and Namiki, Shigehiro and Card, Gwyneth M} } @article {45165, title = {A spike-timing mechanism for action selection.}, journal = {Nature Neuroscience}, volume = {17}, year = {2014}, month = {2014 Jul 17}, pages = {962-70}, abstract = {

We discovered a bimodal behavior in the genetically tractable organism Drosophila melanogaster that allowed us to directly probe the neural mechanisms of an action selection process. When confronted by a predator-mimicking looming stimulus, a fly responds with either a long-duration escape behavior sequence that initiates stable flight or a distinct, short-duration sequence that sacrifices flight stability for speed. Intracellular recording of the descending giant fiber (GF) interneuron during head-fixed escape revealed that GF spike timing relative to parallel circuits for escape actions determined which of the two behavioral responses was elicited. The process was well described by a simple model in which the GF circuit has a higher activation threshold than the parallel circuits, but can override ongoing behavior to force a short takeoff. Our findings suggest a neural mechanism for action selection in which relative activation timing of parallel circuits creates the appropriate motor output.

}, issn = {1546-1726}, doi = {10.1038/nn.3741}, author = {von Reyn, Catherine R and Breads, Patrick and Peek, Martin Y and Zheng, Grace Zhiyu and Williamson, W Ryan and Yee, Alyson L and Leonardo, Anthony and Card, Gwyneth M} }