  In the intact brain, neural activity can be recorded using sensing electrodes
and manipulated using light stimulation. Silicon probes with integrated
electrodes and micro-LEDs enable the detection and control of neural activity
using a single implanted device. Miniaturized solutions for recordings from
small freely moving animals are commercially available, but stimulation is
driven by large, stationary current sources. We designed and fabricated a
current source chip and integrated it into a headstage PCB that weighs 1.37 g.
The proposed system provides 10-bit resolution current control for 32 channels,
driving micro-LEDs with up to 4.6 V and sourcing up to 0.9 mA at a refresh rate
of 5 kHz per channel. When calibrated against a micro-LED probe, the system
allows linear control of light output power, up to 10 micro-W per micro-LED. To
demonstrate the capabilities of the system, synthetic sequences of neural
spiking activity were produced by driving multiple micro-LEDs implanted in the
hippocampal CA1 area of a freely moving mouse. The high spatial, temporal, and
amplitude resolution of the system provides a rich variety of stimulation
patterns. Combined with commercially available sampling headstages, the system
provides an easy to use back-end, fully utilizing the bi-directional potential
of integrated opto-electronic arrays.
