Fast modulation of visual perception by basal forebrain cholinergic neurons

Abstract

The basal forebrain provides the primary source of cholinergic input to the cortex, and it has a crucial function in promoting wakefulness and arousal. However, whether rapid changes in basal forebrain neuron spiking in awake animals can dynamically influence sensory perception is unclear. Here we show that basal forebrain cholinergic neurons rapidly regulate cortical activity and visual perception in awake, behaving mice. Optogenetic activation of the cholinergic neurons or their V1 axon terminals improved performance of a visual discrimination task on a trial-by-trial basis. In V1, basal forebrain activation enhanced visual responses and desynchronized neuronal spiking; these changes could partly account for the behavioral improvement. Conversely, optogenetic basal forebrain inactivation decreased behavioral performance, synchronized cortical activity and impaired visual responses, indicating the importance of cholinergic activity in normal visual processing. These results underscore the causal role of basal forebrain cholinergic neurons in fast, bidirectional modulation of cortical processing and sensory perception.

Figure 1

Optogenetic activation of basal forebrain cholinergic neurons in awake mice. (a) Schematic illustration of experimental setup. (b) Fluorescence microscopy of basal forebrain cholinergic cells expressing ChR2 and EYFP. Asterisk indicates position of optic fiber and arrowheads indicate the posterolateral and anteromedial borders of basal forebrain (nucleus basalis). (c) ChAT immunohistochemistry in basal forebrain of a ChAT-ChR2-EYFP mouse. (d) Example LFP and running speed traces from 3 trials showing the effect of basal forebrain stimulation (blue bar). (e) Top: LFP spectra averaged from experiments in 14 different mice, 30 trials/mouse. Blue bar, laser stimulation. Power at each frequency was normalized by the baseline (5-s period preceding laser onset) and color-coded (scale bar on the right). Middle: time course of desynchronization ratio normalized by the baseline. Bottom: average running speed. Gray shading, ± s.e.m. BF: basal forebrain.

Figure 2

Optogenetic activation of basal forebrain cholinergic neurons or their axons in V1 improved visual discrimination. (a) Schematic illustration of behavioral task. (b) d’ of an example ChAT-ChR2-EYFP mouse in laser on and laser off trials for an basal forebrain activation experiment (3 days, 1,048 trials). Error bars, ± s.e.m. (bootstrap). (c) Population average of d’ (left) and hit and false alarm (FA) rates (right) in laser on and laser off trials for basal forebrain activation experiments. Error bars, ± s.e.m. (d) d’ of an example mouse in laser on and laser off trials for a V1 stimulation experiment (3 days, 614 trials). (e) Population average of d’ (left) and hit and false alarm rates (right) in laser on and laser off trials for V1 stimulation experiments. BF: basal forebrain, FA: false alarm.

Figure 3

Effects of basal forebrain activation on V1 neuronal responses to drifting gratings. (a) Sine-wave gratings of 20%, 40% and 100% contrasts. (b) Top and middle: spike trains of a single unit responding to 100% contrast drifting grating during 20 control (black) and 20 basal forebrain activation (blue) trials. Bottom: corresponding PSTHs for control (black) and basal forebrain activation (blue) trials. Gray dashed line indicates stimulus onset. (c) Population average of firing rates vs. contrast for control (black) and basal forebrain activation (blue) trials. (d) Classification accuracy of grating orientation from an ROC analysis with and without basal forebrain activation. BF: basal forebrain, FR: firing rate.

Figure 4

Effects of basal forebrain activation on V1 neuronal responses to natural movies. (a) Example frames of natural movies. (b) Spike trains of a single unit in response to 30 repeats of a natural movie during control and basal forebrain activation conditions. (c) Spike trains of 15 simultaneously recorded single units in a single trial of natural movie presentation. Note the decrease in correlation between neurons in basal forebrain activation trials. (d) Fano factor in response to natural movies for all driven units (open gray circles), basal forebrain on vs. control, measured at a bin size of 100ms. Error bars indicate s.e.m. (e) Population average of single unit vs. multi-unit coherence with or without basal forebrain activation. Dashed lines, baseline coherence levels calculated from trial shuffles (blue: basal forebrain on, black: control). Error bars and shaded areas, ± s.e.m. BF: basal forebrain, FF: Fano factor.

Figure 5

Basal forebrain cholinergic inactivation synchronizes cortical LFP and impairs behavioral performance. (a) ChAT immunohistochemistry in basal forebrain of a ChAT-ARCH-GFP mouse. (b) Top: LFP spectra averaged from 7 mice (30 trials/mouse). Green bar, laser stimulation. Power at each frequency was normalized by the baseline and color-coded (scale bar on the right). Bottom: average running speed. Shading, ± s.e.m. (c) d’ of an example ChAT-ARCH-GFP mouse in laser on and laser off trials for an basal forebrain inactivation experiment (3 days, 1,101 trials). Error bars, s.e.m. (bootstrap). (d) Population average of d’ in laser on and laser off trials for basal forebrain inactivation. Error bars, ± s.e.m. (green: basal forebrain off, black: control). BF: basal forebrain.

Figure 6

Effects of optogenetic inactivation of basal forebrain cholinergic cells on V1 responses. (a) Spike trains of a simple cell in response to a grating at 100% contrast in 20 control (top panels) and 20 basal forebrain inactivation trials (bottom panels). Note the decrease in firing rate in basal forebrain inactivation trials. Dashed lines indicate stimulus onset. (b) Spike trains of an example single unit in response to natural movie stimuli. Note the decrease in trial-to-trial response reliability with basal forebrain inactivation. (c) Spike trains of 10 simultaneously recorded single units in a single trial of natural movie presentation (control: top, basal forebrain inactivation: bottom). Note the increase in correlated firing between neurons. (d) Firing rate vs. contrast of grating stimuli for control and basal forebrain inactivation trials. (e) Fano factor in response to natural movies for all driven units (open gray circles), basal forebrain off vs. control, measured at a bin size of 100 ms. Error bars indicate s.e.m. (f) Population average of single unit vs. multi-unit coherence with and without basal forebrain inactivation. Dashed lines, baseline coherence levels calculated from trial shuffles (green: basal forebrain off, black: control). Shading, ± s.e.m. BF: basal forebrain, FF: Fano factor, FR: firing rate.