Sensory Processing to Sequential Action Control

Author

Durafshan Sakeena Syed

Module 3 Instructor Guide — Sensory Processing to Sequential Action Control

Conceptual Framework

  • Sensory-driven activation – mechanosensory input triggers grooming behavior
  • Command-like neuron activation – specific neural populations bias or initiate motor programs
  • Hierarchical suppression – competing actions are organized into structured sequences

Students investigate how these levels interact to produce ordered, flexible grooming behavior in Drosophila melanogaster.

Pedagogical Approach

  • Observation – record natural grooming behavior
  • Quantification – annotate and measure sequences
  • Manipulation – test causal roles using optogenetics
  • Interpretation – relate behavior to neural circuits

Learning Objectives

  • Describe hierarchical organization of motor behavior
  • Quantify behavioral sequences using time sampling
  • Compare sensory-driven vs circuit-driven activation
  • Interpret behavioral data in neural circuit context
  • Evaluate selection and suppression of competing motor programs

Suggested Teaching Timeline (2–3 hours)

  • 20 min: Introduction & Background
  • 40 min: Data Collection (Dusting & Optogenetics)
  • ~60 min: Data Analysis (Scoring & Graphing)
  • 30 min: Discussion & Interpretation

Experimental Overview

Conditions

  • Dust stimulation – natural mechanosensory activation
  • Optogenetic activation – artificial activation of neurons

Key Experimental Question

  • How do sensory input and specific neurons influence grooming sequence, timing, and selection?

Expected Outcomes

  • Grooming follows an anterior → posterior progression
  • Head grooming often occurs first
  • Behavioral sequences are structured, not random

Optogenetic activation can:

  • Induce specific actions in clean flies
  • Override ongoing grooming sequences
  • Alter timing and transition probabilities

Variability across flies is expected and can be used to discuss biological variability and experimental noise.

Data Analysis Options

  • Level 1 (Introductory): manual sampling, % time, bar graphs
  • Level 2 (Intermediate): frame scoring, ethograms, transition analysis
  • Level 3 (Advanced): MATLAB/Python, transition matrices, automated classification

Optional statistics:

  • Mann–Whitney U test (between groups)
  • Paired t-test (within-fly comparisons)

Common Pitfalls & Troubleshooting

  • Weak optogenetic activation → check retinal feeding and light conditions
  • Scoring inconsistencies → enforce “dominant behavior per second” rule
  • High variability → expected; use as discussion point

Key Conceptual Takeaways

  • Grooming is hierarchical, not a simple reflex
  • Sensory input biases but does not fully determine behavior
  • Command neurons can initiate and dominate actions
  • Sequences emerge from competition and suppression
  • Motor control is dynamic and flexible

Preparation

Genetic crosses and fly husbandry (~15 days before the experiment)

Fly stocks:

For optogenetic (or thermogenic) experiments: Use flies carrying UAS-CsChrimson (for optogenetics) or UAS-TrpA1 (for thermogenetics).

These need to be crossed with GAL4 or Split-GAL4 driver lines.

Virgin Collection (for setting up crosses):

  1. Identify virgins directly: Collect newly eclosed females (wings still folded, no sex combs on legs).
  2. Alternative method (for beginners):
    • Collect pupae and place a single pupa per vial.
    • After eclosion, identify males and females.
    • All females eclosed in individual vials will be virgins (since no males were present).
    • These vials may also contain unfertilized eggs laid by virgin females.
TipTip

The largest number of virgins will eclose in the morning

Drosophila Workers Unite! is an excellent resource by Michele Markstein on how to do fly pushing/identifying gender differences/virgins and setting up the crosses.

Setting Up Crosses:

  1. Collect males from the desired GAL4 or Split-GAL4 driver lines.
  2. Place 6 virgin females (from UAS-CsChrimson or UAS-TrpA1) and 3–6 males (from a given driver line) together in one vial with fly food.
  3. Maintain at room temperature (or recommended growth temperature for your experiment).

Transferring Parents

Transfer parent flies into new food vials every 5 days. This prevents the parental generation from mixing with the first generation of progeny.

TipTip

To separate flies safely, you can immobilize/anesthetize them by placing the vial on ice or in the refrigerator for ~1 minute.

Collecting Experimental Flies

Collect males from the first-generation progeny (correct genotype) for experiments. These flies will be ready for dusting or optogenetic/thermogenetic activation experiments.

Fly stocks:

Fly Genotype Source Cat#
Iav GAL4 Bloomington Stock Center (BDSC)
R38B08 GAL4 BDSC
DNg12 BDSC
DNg11 BDSC
MagoNote BDSC/Simpson lab
wPN BDSC/Simpson lab
UASCsChrimson BDSC
UAS TrpA1 BDSC
AD-DBD-empty SPLIT BDSC
Canton S BDSC

Preparing flies for experiment (~3 days before the experiment)

Perform behavioral experiments on flies that are 3–6 days old after eclosion.

Control Flies (Wild-Type or Non-Optogenetic): These can be used directly for dusting experiments without any special preparation.

Experimental Flies (Optogenetic with CsChrimson):

Flies carrying UAS-CsChrimson must be fed on retinal-containing food for 3 days prior to the experiment. Retinal is required to make the Chrimson channel sensitive to light activation.