Neural activation increases blood flow locally. This vascular signal is used by functional imaging techniques to infer the location and strength of neural activity 1,2 . However, the precise spatial scale over which neural and vascular signals are correlated is unknown. Furthermore, the relative role of synaptic and spiking activity in driving hemodynamic signals is controversial [3][4][5][6][7][8][9] . Prior studies recorded local field potentials (LFPs) as a measure of synaptic activity together with spiking activity and low-resolution hemodynamic imaging. Here we used two-photon microscopy to measure sensory-evoked responses of individual blood vessels (dilation, blood velocity) while imaging synaptic and spiking activity in the surrounding tissue using fluorescent glutamate and calcium sensors. In cat primary visual cortex, where neurons are clustered by their preference for stimulus orientation, we discovered new maps for excitatory synaptic activity, which were organized similar to spiking activity but were less selective for stimulus orientation and direction. We generated tuning curves for individual vessel responses for the first time and found that parenchymal vessels in cortical layer 2/3 were orientation selective. Neighboring penetrating arterioles had different orientation preferences. Pial surface arteries in cats, as well as surface arteries and penetrating arterioles in rat visual cortex (where orientation maps do not exist 10 ), responded to visual stimuli but had no orientation selectivity. We integrated synaptic or spiking responses around individual parenchymal vessels in cats and established that the vascular and neural responses had the same orientation preference. However, synaptic and spiking responses were more selective than vascular responses-vessels frequently responded robustly to stimuli that evoked little to no neural activity in the surrounding tissue. Thus, local neural and hemodynamic signals were partly decoupled. Together, these results indicate that intrinsic cortical properties, such as propagation of vascular dilation between neighboring columns, need to be accounted for when decoding hemodynamic signals.To determine how neural activity leads to changes in cerebral blood flow, the hemodynamic responses of individual vessels need to be compared to neural activity in the surrounding tissue 11 . While sensory-evoked responses of individual vessels have been measured in the Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
We demonstrate that Alexa Fluor 633 hydrazide (Alexa Fluor 633) selectively labels neocortical arteries and arterioles by binding to elastin fibers. We measured sensory stimulus–evoked arteriole dilation dynamics in mouse, rat and cat visual cortex using Alexa Fluor 633 together with neuronal activity using calcium indicators or blood flow using fluorescein dextran. Arteriole dilation decreased fluorescence recorded from immediately underlying neurons, representing a potential artifact during neuronal functional imaging experiments.
The dorsolateral striatum (DLS) is essential for motor and procedure learning, but the role of DLS spiny projection neurons (SPNs) of direct and indirect pathways, as marked, respectively, by D1 and D2 receptor (D1R and D2R) expression, remains to be clarified. Long-term two-photon calcium imaging of the same neuronal population during mouse learning of a cued leverpushing task revealed a gradual emergence of distinct D1R and D2R neuronal ensembles that reproducibly fired in a sequential manner, with more D1R and D2R neurons fired during the leverpushing period and intertrial intervals (ITIs), respectively. This sequential firing pattern was specifically associated with the learned motor behavior, because it changed markedly when the trained mice performed other cued motor tasks. Selective chemogenetic silencing of D1R and D2R neurons impaired the initiation of learned motor action and suppression of erroneous lever pushing during ITIs, respectively. Thus, motor learning involves reorganization of DLS neuronal activity, forming stable D1R and D2R neuronal ensembles that fired sequentially to regulate different aspects of the learned behavior. striatum | spiny projection neurons | motor learning | calcium imaging | sequence firing T he dorsolateral striatum (DLS) plays an essential role in motor and procedure learning (1-4). The learning process could be divided into cognitive, associative, and autonomous stages (5). In such a scheme, learning begins with a rapid improvement in performance, followed by gradual refinement, until the motor skills become consolidated into long-lasting autonomous actions (6-8). The DLS integrates information from the motor cortex, thalamus, and substantia nigra pars compacta during motor action, motor learning, and habit formation. Studies using progressive depletion of dopamine neurons in mice showed that neurons in the dorsal striatum represent movement vigor (9). Electrophysiogical recording from the striatum while the rat was performing a well-trained treadmill-running task also indicates that DLS neurons may code for the running speed, position, and timing of motor actions (10). During different phases of the mouse's learning of a rotarod task, region-specific changes in dorsal striatal activity have been observed (11). In rats that had learned to perform a T-maze task, there were widely distributed changes in activity patterns of DLS neurons, suggesting the role of the DLS in building a neural representation of habit (12). The striatum consists of mainly two types of spiny projection neurons (SPNs) that differ in their axon projection patterns. The SPNs of the direct pathway express the D1 dopamine receptor (D1R) and send projections to the internal segment of the globus pallidus (GPi) and substantia nigra pars reticulata (SNr), whereas those of the indirect pathway express the D2 dopamine receptor (D2R) and project to the external segment of the globus pallidus (GPe) (13,14). The traditional rate model suggests that activation of the direct pathway promotes movement, while that...
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