# Wired to Rest - Neural Architecture of Sleep States
Lakshman Abhilash

## Background

Sleep is arguably one of the most ubiquitous, yet mysterious behaviors
observed across animal phylogenies. What is sleep? How does one measure
it? Do animals other than mammals have sleep-stage-like states, and if
so, are the molecular and circuit-level mechanisms that regulate these
states known? Are sleep states regulated differently by the circadian
clock and by homeostatic processes? And what do we even mean by
“circadian” and “homeostatic” regulation in the first place? Do males
and females sleep differently, and if so, how is that difference encoded
at the molecular or circuit level?

These questions sit at the intersection of ***neuroscience***,
***genetics***, ***animal behavior***, and ***data science***.
*Drosophila* has long served as a powerful genetic model for dissecting
the functional and circuit-level underpinnings of behavior. A central
conceptual bridge, and a central inquiry driving this module, is how fly
sleep research can be elevated to meaningfully inform mammalian
neuroscience.

## Experimental Preparation

**System and materials.**

The primary experimental platform in this module is the Drosophila
Activity Monitor (DAM) system, manufactured by [Trikinetics
Inc.](https://trikinetics.com) (Waltham, MA).

1.  Individual adult flies are loaded into 5mm glass tubes containing
    sucrose-agar food at one end and sealed at the other with a small
    piece of white yarn, which permits gas exchange while preventing the
    flies from escaping.
    1)  Sucrose-agar food can be made using the following recipe. For
        125mL of food, mix the following in a 1000mL conical flask:
        1)  *125mL de-ionized water.*
        2)  *2.5g Bactoagar.*
        3)  *5g of sucrose.*
    2)  Microwave the mixture until completely dissolved. The solution
        should be transparent and have a yellow/golden color. Keep an
        eye to avoid spills.
    3)  Pour the mixture into a glass petri-dish. Make bundles of
        locomotor tubes with ~35 tubes per bundle. *Note. These tubes
        must be 65mm long and have a diameter of 5mm.*
    4)  These bundles are then dipped into the glass petri-dish with the
        media. Food rises up the tubes through capillary action.
2.  Each loaded tube is inserted into a DAM monitor, which houses 32
    tubes arranged in a grid, with a single infrared (IR) beam passing
    transversally through each tube.
3.  The DAM monitors are then connected to a recording computer as per
    instructions from [Trikinetics Inc.](https://trikinetics.com).

**Experimental logic.**

Every time a fly interrupts its beam, the event is registered by the
recording computer as a unit of locomotor activity, binned in 1-minute
intervals across the full duration of the experiment. This is an elegant
example of engineering in service of biology: a highly reliable,
automated system capable of resolving the fine temporal structure of
behavioral regulation across large numbers of animals simultaneously.

**Protocol design.**

The experimental protocol spans 14 days and is structured in two phases
that together allow circadian and homeostatic regulation of sleep to be
dissected independently.

1.  Days 1 to 4 (entrainment): Monitors are placed in a controlled
    environment (an incubator) under a 12:12 Light:Dark (LD) cycle and
    25 degrees Celsius. The external light-dark cycle entrains flies’
    circadian clocks and provides the temporal reference necessary to
    assess sleep bout timing, phase, and proxies of sleep depth,
    analogous to how polysomnography or wearable consumer devices infer
    sleep-stage architecture from continuous physiological recordings in
    humans.
2.  Days 5 to 14 (free-running): Monitors are transferred to constant
    darkness (DD). This is done by switching the environment in the
    incubator without disturbing the monitors. In the absence of
    environmental timing cues, the free-running, endogenously driven
    circadian regulation of sleep states can be isolated and quantified
    without the confound of environmental influence.

This LD-to-DD transition is a foundational paradigm in chronobiology,
giving students direct, hands-on experience with one of the most
powerful experimental strategies for separating clock-driven from
environmentally modulated behavioral outputs in a concrete application
of controlled experimental design, as foregrounded in NGSS practices.