Transcriptional Landscape of the Prenatal Human Brain

Summary The anatomical and functional architecture of the human brain is largely determined by prenatal transcriptional processes. We describe an anatomically comprehensive atlas of mid-gestational human brain, including de novo reference atlases, in situ hybridization, ultra-high resolution magnetic resonance imaging (MRI) and microarray analysis on highly discrete laser microdissected brain regions. In developing cerebral cortex, transcriptional differences are found between different proliferative and postmitotic layers, wherein laminar signatures reflect cellular composition and developmental processes. Cytoarchitectural differences between human and mouse have molecular correlates, including species differences in gene expression in subplate, although surprisingly we find minimal differences between the inner and human-expanded outer subventricular zones. Both germinal and postmitotic cortical layers exhibit fronto-temporal gradients, with particular enrichment in frontal lobe. Finally, many neurodevelopmental disorder and human evolution-related genes show patterned expression, potentially underlying unique features of human cortical formation. These data provide a rich, freely-accessible resource for understanding human brain development

Optogenetics in Mice Performing a Visual Discrimination Task: Measurement and Suppression of Retinal Activation and the Resulting Behavioral Artifact.

Optogenetic techniques are used widely to perturb and interrogate neural circuits in behaving animals, but illumination can have additional effects, such as the activation of endogenous opsins in the retina. We found that illumination, delivered deep into the brain via an optical fiber, evoked a behavioral artifact in mice performing a visually guided discrimination task. Compared with blue (473 nm) and yellow (589 nm) illumination, red (640 nm) illumination evoked a greater behavioral artifact and more activity in the retina, the latter measured with electrical recordings. In the mouse, the sensitivity of retinal opsins declines steeply with wavelength across the visible spectrum, but propagation of light through brain tissue increases with wavelength. Our results suggest that poor retinal sensitivity to red light was overcome by relatively robust propagation of red light through brain tissue and stronger illumination of the retina by red than by blue or yellow light. Light adaptation of the retina, via an external source of illumination, suppressed retinal activation and the behavioral artifact without otherwise impacting behavioral performance. In summary, long wavelength optogenetic stimuli are particularly prone to evoke behavioral artifacts via activation of retinal opsins in the mouse, but light adaptation of the retina can provide a simple and effective mitigation of the artifact

Behavioral artifact of deep brain illumination.

<p>(A) Schematic illustration of the implanted guide cannula, fiber and deep brain illumination. Drawn approximately to scale. (B) Schematic illustration of the fiber implant (red circle) viewed from the dorsal surface of the head, illustrating the position of the fiber relative to the eyes. (C) Mean running speed trajectory for a single session in which 50% of trials included 640 nm illumination. Rewarded and unrewarded objects were presented at 100% contrast with (red traces) and without (black traces) 640 nm illumination. (D) Summary of performance during the session illustrated in panel B. Trials with and without 640 nm illumination are illustrated with red and black vertical bars, respectively. (E) Stop probabilities for the session illustrated in panel C. (F) Psychometric curves for a single wild-type mouse across four sessions, with different deep brain illumination in each session: no deep brain illumination (left panel), 10 mW of 473 nm illumination (center left), 10 mW of 589 nm illumination (center right), 10 mW of 640 nm illumination (right). Each session included trials with (colored symbols and lines) and without (black, grey) illumination. Stop probabilities for rewarded and unrewarded trials are illustrated with darker and lighter colors, respectively. (G) Stop probabilities for zero-contrast objects (false alarm rates) for 1, 3 and 10 mW at 473 (blue), 589 (yellow) and 640 nm (red) illumination. Results for each intensity and wavelength were collected in a different session and compared to the stop probability without illumination in the same session (in black). Asterisks denote significant effects of illumination (p < 0.01). Numbers of mice: 6, 8 and 8 mice for 1, 3 and 10 mW of 473 nm illumination; 6, 5 and 6 mice for 1, 3 and 10 mW of 589 nm illumination; 4, 5 and 5 mice for 1, 3 and 10 mW of 640 nm illumination. (H) Reward rate under illuminated and control conditions, within the same session. Results from individual mice are illustrated in grey, mean ± SEM of 5 mice in black. Rewards summed across rewarded and unrewarded objects of all contrasts; numbers of trials of each contrast with and without illumination were approximately equal.</p

Performance across a range of contrasts.

<p>(A) Mean running speed trajectories, for a single session, for objects of contrasts from 0 to 100%, rewarded (upper row) and unrewarded (lower row) objects. Dashed vertical lines: limits of reward window. (B) Psychometric curves for rewarded (vertical) and unrewarded (horizontal) objects for the session illustrated in panel A. Line, fit to Weibull distribution; error bars, 95% confidence intervals. (C) Discriminability of rewarded and unrewarded objects as a function of contrast. Each point is the mean (± SEM) from 6 mice.</p

Light adaptation of left and right retinae.

<p>(A) Schematic illustrating the experimental arrangement of mouse head, visual stimulus monitor and LED, the latter placed to illuminate the left retina. (B) Example ERG recordings from left and right eyes of a mouse under different ambient illumination conditions: monitor and LED off (dark-adapted; top row); monitor on and LED off (middle row), and monitor and LED both on (lower row). Optogenetic stimulus was 200 ms, 10 mW, 640 nm illumination (grey). (C) Summary of the effects of LED illumination on the peak amplitude of the ERG voltage in different adaptation states. Left point (dark-adapted) with monitor and LED off. Remaining points were acquired with the monitor on and the LED providing differing illumination intensities. Points represent mean ± SEM (3 mice). Arrowhead marks 0.14 Wsr^-1m^-2.</p

Measurement of light exiting the left eye.

<p>(A) Schematic illustrating the experimental arrangement during measurement of light emitted through the left eye. Light (red arrow) propagated from the implanted fiber (red circle) to a spectroradiometer, placed in front of the left eye. (B) Intensities measured by the spectroradiometer during 10 mW illumination through the implanted fiber at 473, 589 and 640 nm. 3 mice.</p

Performance of a visual discrimination task.

<p>(A) Schematic illustration of visual discrimination task. The mouse is head-restrained, on a running disk. Visual objects, displayed on a monitor, travel along the horizon from left to right. (B) Schematic illustration of the relative positions of mouse and monitor. (C) Running speed as a function of distance run by the mouse in two example trials. The position of the monitor, object and reward window are drawn to scale on the distance axis. (D) Summary of performance during a single example session, plot over time from the start to the end of the session (from left to right). Vertical lines indicate trials, sorted into four categories by object (rewarded vs unrewarded) and behavioral response (detected and undetected objects). The mouse collected rewards only on trials in which it indicated detection of a rewarded object (uppermost category). (E) Mouse-to-mouse and session-to-session variability in stop probability for rewarded and unrewarded objects and in discriminability (d'). Results are for 6 mice (rows) and across 6 sessions (columns).</p