# Developmental Logic as Circuit Blueprint.
Jelly Soffers

## Part 1: Lineage-Specific Optogenetic Activation in the Drosophila Ventral Nerve Cord

### Overview

How does the nervous system build circuits that produce specific
behaviors?

In this module, you will investigate whether groups of neurons that
develop together also work together to control behavior.

In the fruit fly (*Drosophila*), neurons are produced in developmental
families called **lineages**. Each lineage typically divides into two
groups called **hemilineages**. Neurons within a hemilineage often share
similar shapes, connections, and roles in the nervous system.

Scientists think that these hemilineages may act as building blocks for
neural circuits. If this idea is correct, then activating different
hemilineages should produce different and predictable behaviors.

To test this hypothesis, you will use **optogenetics**—a technique that
allows neurons to be activated with light. By stimulating specific
neuronal populations in the ventral nerve cord (VNC), you will observe
how flies respond and determine whether developmental identity can
predict behavioral output.

In the figure below you can see how the neuronal cell bodies and axonal
projects cover different regions in the fly’s spinal cord. THe neurons
that light up i ngreen are the same neurosn as you will be activating in
real life!

<div id="fig-lines">

<div id="fig-lines-a">

<img src="assets/module01/lines_a.png" id="fig-lines-a"
data-ref-parent="fig-lines" />

(a)

</div>

<div id="fig-lines-b">

<img src="assets/module01/lines_b.png" id="fig-lines-b"
data-ref-parent="fig-lines" />

(b)

</div>

Figure 1: GAL4 lines

</div>

In the video’s below you see our video recordigns of these and some more
hemilineages. Click on the links and pay attention to the differences.

<div id="fig-behavior">

<div id="fig-behavior-a">

<video src="assets/module01/Video-5B-1.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-5B-1.mp4">Video</a></video>

(a) Line 5B, example 1

</div>

<div id="fig-behavior-b">

<video src="assets/module01/Video-5B-2.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-5B-2.mp4">Video</a></video>

(b) Line 5B, example 2

</div>

<div id="fig-behavior-c">

<video src="assets/module01/Video-5B-3.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-5B-3.mp4">Video</a></video>

(c) Line 5B, example 3

</div>

<div id="fig-behavior-d">

<video src="assets/module01/Video-5B-4.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-5B-4.mp4">Video</a></video>

(d) Line 5B, example 4

</div>

<div id="fig-behavior-e">

<video src="assets/module01/Video-14A-1.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-14A-1.mp4">Video</a></video>

(e) Line 14A, example 1

</div>

<div id="fig-behavior-f">

<video src="assets/module01/Video-14A-2.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-14A-2.mp4">Video</a></video>

(f) Line 14A, example 2

</div>

<div id="fig-behavior-g">

<video src="assets/module01/Video-17A-1.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-17A-1.mp4">Video</a></video>

(g) Line 17A, example 1

</div>

<div id="fig-behavior-h">

<video src="assets/module01/Video-17A-2.mp4"
data-ref-parent="fig-behavior" controls=""><a
href="assets/module01/Video-17A-2.mp4">Video</a></video>

(h) Line 17A, example 2

</div>

Figure 2: Behavior

</div>

Now it is time to investigate the flies in front of you.

### Step 1: Observe

Before applying light stimulation:

- Observe the flies for 1–2 minutes.
- Record their normal behavior.
- Discuss with your group what behaviors you might expect if specific
  neural circuits were activated.

### Step 2: Activate the Circuit

Using the light source provided:

1.  Illuminate the flies.
2.  Observe the behavioral response.
3.  Repeat the stimulation several times.
4.  Record whether the response is consistent across trials.

### Step 3: Describe What You See

Focus on observations rather than interpretations.

Examples could be

- Walking forward
- Full leg stretching
- Backward movement
- Turning
- Wing buzzing
- Jumping
- Wing extension
- Freezing
- Grooming-like movements

Record your observations in a table similar to the one below.

| Trial | Observed Behavior | Consistent? | Notes |
|-------|-------------------|-------------|-------|
| 1     |                   |             |       |
| 2     |                   |             |       |
| 3     |                   |             |       |

### Step 4: Compare Results

Share your observations with other groups.

Look for patterns:

- Which fly lines produced similar behaviors?
- Which produced distinct behaviors?
- Were some responses stronger or more reliable than others?

### Think Like a Neuroscientist

If activating a particular neuronal population repeatedly produces the
same behavior:

- What does this suggest about its role in the nervous system?
- What can behavior tell us about circuit organization?
- What information cannot be determined from activation experiments
  alone?

### Discussion Questions

1.  Did different fly lines produce distinct behaviors?
2.  Were the behaviors reproducible?
3.  Which behaviors appeared to involve simple motor outputs versus more
    complex action sequences?
4.  What evidence supports the idea that developmental identity
    influences neural function?
5.  What additional experiments would be needed to determine whether
    these neurons are necessary for a behavior, rather than simply
    capable of producing it when activated?