3 research outputs found
Bidirectional optogenetic control of inhibitory neurons in freely-moving mice
Objective: Optogenetic manipulations of excitable cells enable activating or
silencing specific types of neurons. By expressing two types of exogenous
proteins, a single neuron can be depolarized using light of one wavelength and
hyperpolarized with another. However, routing two distinct wavelengths into the
same brain locality typically requires bulky optics that cannot be implanted on
the head of a freely-moving animal.
Methods: We developed a lens-free approach for constructing dual-color
head-mounted, fiber-based optical units: any two wavelengths can be combined.
Results: Here, each unit was comprised of one 450 nm and one 638 nm laser
diode, yielding light power of 0.4 mW and 8 mW at the end of a 50 micrometer
multimode fiber. To create a multi-color/multi-site optoelectronic device, a
four-shank silicon probe mounted on a microdrive was equipped with two
dual-color and two single-color units, for a total weight under 3 g. Devices
were implanted in mice expressing the blue-light sensitive cation channel ChR2
and the red-light sensitive chloride pump Jaws in parvalbumin-immunoreactive
(PV) inhibitory neurons. The combination of dual-color units with recording
electrodes was free from electromagnetic interference, and device heating was
under 7{\deg}C even after prolonged operation.
Conclusion: Using these devices, the same cortical PV cell could be activated
and silenced. This was achieved for multiple cells both in neocortex and
hippocampus of freely-moving mice.
Significance: This technology can be used for controlling spatially
intermingled neurons that have distinct genetic profiles, and for controlling
spike timing of cortical neurons during cognitive tasks.Comment: 11 pages, 9 figure
Outan: An On-Head System for Driving micro-LED Arrays Implanted in Freely Moving Mice
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.Comment: 11 pages, 9 figure
Positive and biphasic extracellular waveforms correspond to return currents and axonal spikes
Abstract Multiple biophysical mechanisms may generate non-negative extracellular waveforms during action potentials, but the origin and prevalence of positive spikes and biphasic spikes in the intact brain are unknown. Using extracellular recordings from densely-connected cortical networks in freely-moving mice, we find that a tenth of the waveforms are non-negative. Positive phases of non-negative spikes occur in synchrony or just before wider same-unit negative spikes. Narrow positive spikes occur in isolation in the white matter. Isolated biphasic spikes are narrower than negative spikes, occurring right after spikes of verified inhibitory units. In CA1, units with dominant non-negative spikes exhibit place fields, phase precession, and phase-locking to ripples. Thus, near-somatic narrow positive extracellular potentials correspond to return currents, and isolated non-negative spikes correspond to axonal potentials. Identifying non-negative extracellular waveforms that correspond to non-somatic compartments during spikes can enhance the understanding of physiological and pathological neural mechanisms in intact animals