The Harley Lab

In my lab we have several ongoing projects. All center around examining how simple nervous systems are able to create complex behaviors. The medicinal leech has 10,000 neurons (we have one billion neurons) and they are still able to locate food, mates, and negotiate complex environments. My goal is to learn how they do these things. Specific projects are as follows:

    1. How does the visual system guide leech behavior?

We are examining how simple visual stimuli influence leech locomotion at the behavioral level. Many animals, from drosophila to humans, have a simple reflex called an optimotor response where they orient toward moving bars. We are trying to determine if this response is present in leeches. There are several theories behind the neural control of this response however their validity cannot be tested on current model systems due to the intrinsic complexity of those systems. If the leech has this response, we could determine how their neurons process this information-- something which could determine which of the current theories is most valid. This work has been presented in poster form.

Leeches have 294 eyes (10 complex and 284 simple), due to technical limitations, no one has ever examined the connections between the complex eyes and cells within the brain. This would aid us both in determining how these cells process visual information and how that response is relayed to neurons that control locomotor behavior.

2. How does physical therapy influence the recovery of a nervous system following injury?

Leeches have two ways of locomoting, they can swim and they can crawl, with the latter being the preferred behavior. When their brain is disconnected from the rest of their nervous system, they lose the ability to crawl and they swim nearly ceaselessly. My work has shown that over time, they recover the ability to crawl and the ability to stop swimming. Now we are examining if by stimulating the sensory system using physical therapy we can expedite the recovery process. How does one perform physical therapy on a leech? With a tiny treadmill outfitted with a silicone mold that challenges the leech to crawl. So far, our results are promising showing animals initiating crawl behavior many days earlier if they have had therapy. This study will enable us to determine the cellular mechanism behind how physical therapy works, something which is not known in any system.


This work could not be done without help, specifically that of my wonderful research students. Their tenacity and creativity is awe inspiring.

Visual Behavior Project

Cynthia Yoder

Brian Chi

Sundus Yusef

Tyler Pinkston

Chee Xiong

Visual Neuroanatomy Project

Marissa Peterson

Linna Ahmado

Physical Therapy Project

Emiliya Bayko

Brandon Young

Andrew Clayburn

Hannah Lee

Alison Aguilar

Jasmine Engler

Alyssa Anderson

Liz Baseka Nemmeh

Kelly Sheehy

Heather Harrington

Adefunke Edon

Darlene Zemke

Arabella Jones

Neira Begic