Supplementary MaterialsSI guide. triggered regenerative events that included dendritic spikes. These

Supplementary MaterialsSI guide. triggered regenerative events that included dendritic spikes. These events were orientation tuned and suppressed by either hyperpolarization or intracellular NMDA receptor blockade. Both of these manipulations also decreased the selectivity of subthreshold orientation tuning measured at the soma, thus linking dendritic regenerative events with somatic orientation tuning. Together, our results suggest that dendritic spikes triggered by visual input contribute to a fundamental cortical computation: enhancing orientation selectivity in visual cortex. Neuronal dendrites express voltage-dependent Ca2+ and Na+ channels that confer electrical excitability, in particular the ability to support active backpropagation of action potentials and the initiation of local dendritic spikes1. In addition, the voltage-dependent Mg2+ block of synaptic NMDA receptors can also support nonlinear synaptic integration and dendritic spike initiation5,10. These mechanisms of active synaptic integration have been probed extensively under some conditions6C8, it remains unclear whether these mechanisms are involved in behaviorally relevant computations11C13. To investigate whether dendritic nonlinearities can contribute to a well-known example of cortical computation, orientation tuning in the visual cortex14, we have made direct dendritic patch clamp recordings from layer 2/3 neurons in mouse visual cortex. To measure dendritic activity = 12) apical dendrites of layer 2/3 neurons in mouse primary visual cortex (Fig. 1a) in lightly anesthetized and awake mice. Cells were filled via the patch pipette with a fluorescent Ca2+ dye (Oregon Green BAPTA-1, 100 M) for imaging Ca2+ transients, and a fluorescent red dye (Alexa 594, 25-50 M) to image the morphology of the dendritic arbor and identify the precise location of the dendritic recording (Fig. 1b). Dendritic recordings exhibited expected physiological features, such as a high local input resistance increasing with distance from the soma (Extended Data Fig. 1a-c)15,16. Open in a separate window Figure 1 Dendritic patch-clamp recordings from visual cortex pyramidal neurons dendritic patch-clamp recordings under two-photon microscopy. b, Two-photon image of a layer 2/3 pyramidal neuron in mouse visual cortex filled with Alexa 594 via a dendritic patch-clamp recording 100 m from the soma (maximum intensity projection). c, Somatic spiking and dendritic activity (d) evoked by presenting square wave grating visual stimuli both exhibited reliable, orientation-tuned burst spiking events. The asterisks mark bAPs. e, Spikes within dendritic burst events were highly variable compared to the more stereotyped bAPs and somatically recorded APs. f, Dendritic burst event frequency varied with CALNA orientation. g, individual burst events were highly variable in amplitude and kinetics (dendritic recording 150 m from the soma). In somatic recordings, visual stimulation with drifting square wave gratings evoked conventional U0126-EtOH distributor action potential activity, with the firing rate tuned to the orientation of the stimulus (Fig. 1c)14,17. By contrast, recordings from distal dendrites ( 75 m from the soma) revealed orientation-tuned, high frequency bursts of Na+ spikes riding on U0126-EtOH distributor a depolarization envelope consistent with activation of voltage-gated Ca2+ channels and synaptic NMDAR currents (Fig. 1d-g, Extended Data Fig. 1d). Their properties contrasted with those of isolated spikes (single spikes separated by at least 50 ms from other spikes), which are presumed to be backpropagating action potentials (bAPs; Fig. 1d, e), though not all bAPs are isolated bAPs. These isolated bAPs exhibited a uniform amplitude and shape within a recording, and decreased in amplitude and increased in width with increasing distance from the soma (Extended Data Fig. 1e-f)15. While dendritic bursts can contain both local Na+ spikes and bAPs, these isolated bAPs provide a readout of somatic activity that can be compared with local dendritic events. Visually evoked spike bursts recorded at the dendrite were tuned to the orientation of the stimulus, with reliable tuning trial-to-trial (Fig. 1e, f). The preferred orientation of bursts was not different from that of bAPs (= 9, difference in preferred orientation: 34.7 28.8; 0.22, paired t-test; Extended Data Fig. 2). We next sought to determine whether these dendritic events were local. Given that Na+ spikes, a prominent feature of the dendritic regenerative events we recorded, have fast kinetics, their waveform is likely to be heavily attenuated by the cable filtering properties of the dendritic arbor, and thus not propagated efficiently to the soma (by contrast, the slow depolarization envelope of dendritic regenerative events can propagate to the soma). U0126-EtOH distributor The maximum instantaneous and mean spike rates, as well as the variance-to-mean ratio, were highest in distal dendritic ( 75 m; = 9) recordings compared to proximal dendritic ( 50 m;.