ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. HyoJong Jang is an author on ‘ Azimuthal invariance to looming stimuli in the Drosophila giant fiber escape circuit’, published in JEB. HyoJong is a postdoc in the lab of Catherine von Reyn at the School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, USA, investigating the mechanisms underlying how the brain recognizes or responds to external inputs using the model organism Drosophila melanogaster.

HyoJong Jang.

Describe your scientific journey and your current research focus

I earned my PhD in Biomedical Engineering, Science and Health Systems from Drexel University, where I explored my research interests in how the brain processes visual information. Before that, I completed my Bachelor's, Master's and PhD degrees in Computer Science from Soongsil University in South Korea, where my studies focused on image processing and pattern recognition. During my computer science studies, I became passionate about understanding how animals perceive their environment, and I ultimately joined the von Reyn lab to pursue this research further. Currently, I use Drosophila melanogaster as a model organism to investigate the underlying mechanisms of how the brain responds to external stimuli.

How would you explain the main finding of your paper to a member of the public?

To survive, animals need to react quickly to changes in their environment. To do this, their brains must receive information from their senses, like what they see or hear, and use that information to decide what to do next. But we still don't know exactly how the brain makes these decisions, because the connections between sensory information and behavior are not fully understood yet. We use the fruit fly Drosophila melanogaster as our model organism to investigate how the brain encodes visual information and transforms it to drive relevant behavior. To investigate how the brain processes visual information and generates motor behavior for escape behavior, we show ‘looming’ stimuli to flies that mimic an object approaching on a direct collision course. In response to looming stimuli, animals can perform a variety of escape behaviors such as freezing, fleeing, jumping and flight initiation. This flexibility has been hypothesized to emerge from parallel pathways that function to select and coordinate a behavioral response. In the fruit fly, each pathway consists of a pair of descending neurons that are thought to be a critical bottleneck in the flow of information from sensory systems in the brain to motor circuits in the ventral nerve cord (the fly ‘spinal cord’). As there is one neuron on each side of the brain, we believed that different information coming in through two eyes is essential for effective avoidance. In our research, we found ipsilateral neurons in some descending neurons (DNp01 which is also known as giant fiber, DNp02 and DNp06) respond to contralateral looming stimuli even though their dendrites are only located on the ipsilateral side of the brain. This implies that there is an unidentified pathway across the midline to communicate between a pair of descending neurons. Interestingly, the giant fiber's response to looming stimuli showed invariance without differences in the response magnitude and latency across the tested azimuthal direction. This invariance seems to be aligned with the giant fiber's role in escape as the giant fiber is known for no directional escape trajectories towards the stimulus location. We also found the illumination level of the contralateral eye modifies the processing of dynamic stimuli in the ipsilateral eye as occluding the contralateral eye changed ipsilateral tuning towards abrupt stimuli. We believe that the occlusion of the contralateral eye may result in a luminance gain modulation or compensatory plasticity in the visual feature pathway.

What are the potential implications of this finding for your field of research, and is there anything that you learned during this study that you wish you had known sooner?

Our results demonstrated that there could be unidentified pathways across both eyes between a pair of descending neurons. This finding expands the potential scope of our study to include the circuitry of both hemispheres of the brain. While previous work has focused on visual processing in the ipsilateral side, we can now explore more detailed tuning properties that may affect the final behavior. For example, we can investigate whether their receptive fields exist within an eye or across both eyes. We can also compare their response timing across the midline if a neuron responds to both sides. As we believe that any distinct characteristics between descending neurons may contribute to various aspects of defensive behaviors, such as postural adjustment or directional escape trajectories, we hope to elucidate how descending neurons interact with each other to coordinate a final, complex escape behavior.

Visual stimulus setup for a tethered fruit fly with in vivo electrophysiology.

Visual stimulus setup for a tethered fruit fly with in vivo electrophysiology.

Are there any important historical papers from your field that have been published in JEB?

Previous work published by Trimarchi and Schneiderman (1995), entitled ‘Different neural pathways coordinate Drosophila flight initiations evoked by visual and olfactory stimuli’ (doi:10.1242/jeb.198.5.1099), reported that there are different neural pathways that coordinate Drosophila flight initiations. They compared two extracellular recordings from the cervical connective nerve during flight initiation: visually elicited flight initiation and olfactory-induced flight initiation. The results showed that the time interval between the spike and the activation of the tergotrochanteral muscle was different between the visually elicited and the olfactory-induced flight initiation. This suggested the existence of an unidentified neural pathway for olfactory-induced flight initiation, which is different from the visually elicited giant fiber pathway. These findings have inspired researchers to investigate alternative pathways in escape initiation in later research.

Are there any modern-day JEB papers that you think will be the classic papers of 2123?

I think that Card and Dickinson's 2008 study, ‘Performance trade-offs in the flight initiation of Drosophila’ (doi:10.1242/jeb.012682), was pioneering research that is highly relevant to our work. They observed two distinct types of flight initiation: a voluntary take-off which is slower and more stable, and a visually evoked take-off which is faster but less stable. This finding could potentially lead us to explore the existence of at least two distinct pathways that contribute to the two types (fast and slow) of escape behavior in Drosophila. Currently, we are expanding our research to investigate the multiple pathways involved in escape behavior. There are multiple pathways of descending neurons that respond to looming stimuli and it is believed that they interact with each other to create complex sequences in initiating an escape behavior.

If you had unlimited funding, what question in your research field would you most like to address?

As the descending neurons related to escape behavior have been thought to interact as a network to drive an appropriate behavior in response to external stimuli, I am primarily interested in investigating their interactions. One promising way to study this could be using the wide-field imaging technique. However, because of existing technological limitations in experimental design for Drosophila, I am interested in investing in the development of a wireless head-mounted microscope device for monitoring the behavior of a specific group of cells in the brain of freely moving fruit flies. The device would be a miniature version of the wireless head-mounted microscope device used in mice. By achieving this, we can observe and record the activity of the cells in the network and we can also apply this to freely moving flies provided with a threat stimulus.

HyoJong Jang's contact details: Drexel University, School of Biomedical Engineering, Science and Health Systems, Philadelphia, PA 19104, USA.

E-mail: hj97@drexel.edu

Jang
,
H.
,
Goodman
,
D. P.
,
Ausborn
,
J.
and
von Reyn
,
C. R
. (
2023
).
Azimuthal invariance to looming stimuli in the Drosophila giant fiber escape circuit
.
J. Exp. Biol.
226
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jeb244790
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