Abstract
Optogenetics has proven to be a revolutionary technology in neuroscience and has advanced continuously over the past decade. However, optical stimulation technologies for in vivo need to be developed to match the advances in genetics and biochemistry that have driven this field. In particular, conventional approaches for in vivo optical illumination have a limitation on the achievable spatio-temporal resolution. Here we utilize a sapphire-based microscale gallium nitride light-emitting diode (μLED) probe to activate neocortical neurons in vivo. The probes were designed to contain independently controllable multiple μLEDs, emitting at 450 nm wavelength with an irradiance of up to 2 W/mm2. Monte-Carlo stimulations predicted that optical stimulation using a μLED can modulate neural activity within a localized region. To validate this prediction, we tested this probe in the mouse neocortex that expressed channelrhodopsin-2 (ChR2) and compared the results with optical stimulation through a fiber at the cortical surface. We confirmed that both approaches reliably induced action potentials in cortical neurons and that the μLED probe evoked strong responses in deep neurons. Due to the possibility to integrate many optical stimulation sites onto a single shank, the μLED probe is thus a promising approach to control neurons locally in vivo.
Highlights
Since the early 2000s (Boyden et al, 2005), optogenetics has become one of the standard experimental techniques in neuroscience (Yizhar et al, 2011; Häusser, 2014)
Characteristics of the μLED Probe The fabricated μLED probe demonstrated high light output, as shown in Figure 1B, with an irradiance at the μLED surface of 2 W/mm2 possible at 6 mA, the light will propagate through the sapphire substrate giving a maximum intensity of 52 mW/mm2 at the tissue/probe interface
We have demonstrated the feasibility of sapphire-based μLED probes for in vivo optogenetic experiments, successfully activating neocortical neurons in vivo
Summary
Since the early 2000s (Boyden et al, 2005), optogenetics has become one of the standard experimental techniques in neuroscience (Yizhar et al, 2011; Häusser, 2014). Neocortical circuits have anatomically prominent six-layered structures, where certain cell-types are distributed across these cortical layers. These neurons can have layer-specific functions, but it is challenging to target them for in vivo. In each of these cases the light sources are located external to the neural tissue and require complex optical components to scale the number of illumination sites. This leads to an expensive and technically challenging system. We (McAlinden et al, 2013) and other groups (Kim et al, 2013; Moser, 2015) have independently proposed μLED technology for in vivo optogenetic experiments
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