Navigation, freezing, and eye movements are three classic behavioral readouts that reveal memory, internal state, and attention — without needing the animal to press a button or lick a spout.

Morris Water Maze — spatial memory:
A mouse is placed in a pool of water with a hidden submerged platform. Initially the mouse swims randomly. After repeated trials, it learns the platform's location relative to visual landmarks on the walls.

After learning: the mouse swims directly to the platform. The readout is the swim path — how quickly and directly it finds the platform. This tests spatial learning and memory (hippocampus-dependent).

Applications: hippocampal lesion studies, Alzheimer's disease models, effects of drugs on memory.

Fear conditioning — internal state:
Mice naturally freeze (stop all movement) when they see a predator. Neuroscientists exploit this:
1. Context conditioning: shock the mouse in an environment → the mouse freezes when returned to that environment days later (it remembered the scary place)
2. Cue conditioning: pair a tone with a shock → the mouse eventually freezes just on hearing the tone (Pavlovian conditioning)

Freezing duration = indirect measure of fear. No surgery required — just a camera measuring movement.

Eye tracking — attention and social cognition:
Tracking exactly where an animal looks reveals what it's paying attention to and how it parses complex scenes.

Example: monkeys were shown images of other monkeys' faces. Eye tracking revealed they spent the most time looking at the eyes — just like humans do when viewing faces. This shows that social attention mechanisms are conserved across primates.

🧠 The goal of all these readouts: pair behavioral data with neural recordings to understand what computations the brain is performing. Behavior is the output we're trying to explain. Neural activity is the mechanism. Behavioral readouts connect the two.