Light was combined by a series of dichroic mirrors and focused onto a 5 mm diameter piece of opal diffusing glass (Edmund Optics Inc., York, UK) positioned <1 mm from the eye (contralateral to the recording probe for LGN recordings).
Once the recording probe was in position mice were dark adapted for 1 h, which also allowed neuronal activity to stabilise after probe insertion/repositioning.
After recording a set of responses at one location the recording probe was raised or lowered by 400 µm and, after 1 h dark adaptation, another set of responses recorded.
A 64-site silicon recording probe (8 shanks, 8 recording sites per shank, 200 µm lateral spacing between shanks, 20 µm vertical spacing between recording sites) was implanted into the dorsal right hippocampal CA1 region under isoflurane anesthesia.
Light stimuli (460 nm; half peak width: ±10 nm), were generated by a custom built LED based light source (Cairn Research Ltd ., passed through neutral density filters as necessary, and was focused onto a 5 mm diameter opal diffusing glass (Edmund Optics Inc., UK) positioned 3 mm from the eye contralateral to the recording probe.
A recording probe (A4X8-5 mm-50-200-413; Neuronexus, MI, USA) consisting of 4 shanks (spaced 200 µm), each with 8 recordings sites (spaced 50 µm) was then positioned centrally on the exposed skull surface, perpendicular to the midline, and lowered to a depth of 2.2 to 3.4 mm using a fluid filled micromanipulator (MO-10; Narishige).
A recording probe was placed on the surface of the eye, and a reference probe was inserted in the thorax.
Briefly, adult flies were glued to a glass slide and a recording probe was placed on the surface of the eye, and a reference probe was inserted in the thorax.
recording probe (A4X8-5 mm-50-200-413; NeUSAnexus, Ann Arbor, Mintroducedtooduced thethe LGN using stereotaxic coordinates (Bregma: −2.5 mm; Midline: −1.9 to −2.5; Depth: −2.6 mm relative to brain surface).
The authors also discuss the use of electrical recording probes: "There are technical hurdles to be surmounted, but when the technology is perfected, recording from many thousands of neurons is conceivable".
