Head-fixed reward delivery

A reward-delivery and lick-sensing module for head-fixed mice under a two-photon microscope. A servo swings a metal lick spout to the animal only during reward, a pinch valve meters the liquid, and BeeHive emits an analogue event signal for alignment with imaging.

Ingredients

BeeHive boards:

Other components:

How it works

The animal is head-fixed under a two-photon microscope and presented with a 10 s visual stimulus. Timing runs as follows:

• −0.5 s (0.5 s before the stimulus ends): the Geekservo begins swinging the metal lick spout towards the animal.
• −0.25 s: the mainboard triggers the solenoid control board, opening the normally-closed pinch valve for 150 ms to deliver a metered drop of liquid.
• The mouse is given 1 s to lick. The piezo lick sensor on the spout registers each contact.
• The spout then retracts out of reach until the next trial.

Throughout, BeeHive emits an analogue voltage signal to an NI DAQ. The voltage level encodes the event type and its duration encodes how long the event lasted, so every reward, spout movement and lick can be aligned post-hoc with the two-photon imaging stream on a common timebase.

Wiring

• Servo signal line to a mainboard data line; servo power from the 5 V rail.
• Piezo lick sensor to a mainboard analogue input.
• Pinch valve to the solenoid control board output; the board takes a data line from the mainboard.
• Analogue event output to NI DAQ analogue input channel, sharing ground with the DAQ.

Code

Delivering a reward comes down to opening the solenoid control board's valve for a fixed time — exactly the BeeHive solenoid driver example (the pins are the board's default outputs):

from machine import Pin
import time

sole1 = Pin(2, Pin.OUT, drive=Pin.DRIVE_3)   # solenoid control board output

sole1.on()
time.sleep_ms(150)     # 150 ms reward pulse
sole1.off()

The full task wraps this valve pulse in the timing described above: a servo swings the spout in ~0.5 s before stimulus offset, the reward pulse follows 0.25 s later, then a 1 s lick window is read from the piezo sensor, with an analogue event signal sent to the DAQ (level = event type, duration = event length). That orchestration is specific to each rig; the reward pulse itself is the repo example above.

Results / notes

The module adds closed-loop reward delivery and lick detection to an existing head-fixed two-photon rig, with events cleanly aligned to imaging via the analogue DAQ signal. The single-spout build extends to two-choice paradigms by duplicating the spout, servo and solenoid channel.