A comprehensive thalamocortical projection map at the mesoscopic level

Abstract

The thalamus relays sensori-motor information to the cortex and is an integral part of cortical executive functions. The precise distribution of thalamic projections to the cortex is poorly characterized, particularly in mouse. We employed a systematic, high-throughput viral approach to visualize thalamocortical axons with high sensitivity. We then developed algorithms to directly compare injection and projection information across animals. By tiling the mouse thalamus with 254 overlapping injections, we constructed a comprehensive map of thalamocortical projections. We determined the projection origins of specific cortical subregions, and verified that the characterized projections formed functional synapses using optogenetic approaches. As an important application, we determined the optimal stereotaxic coordinates for targeting specific cortical sub-regions and expanded these analyses to localize layer-preferential projections. This dataset will serve as a foundation for functional investigations of thalamocortical circuits. Our approach and algorithms also provide an example for analyzing the projection patterns of other brain regions.

Stroke and the Connectome: How Connectivity Guides Therapeutic Intervention

“…These regions could include those that receive common thalamic input or send axonal projections to neighboring targets. For example, motor cortex, primary somatosensory cortex, and secondary somatosensory cortex all receive thalamic input (Hunnicutt et al, 2014;Oh et al, 2014), and function in secondary areas can be preserved after stroke to primary somatosensory areas (Sweetnam and Brown, 2013). In the rodent motor cortex, for example, the strongest intracortical connections are with the rest of the sensory-motor cortex in the same hemisphere, but strong interhemispheric connections also exist with homotopic areas (Bauer et al, 2014).…”

Connectomic Analysis of Brain Networks: Novel Techniques and Future Directions

“…The results were imaged using serial two-photon tomography, an imaging tool discussed later in this review. The resulting open-access mesoscale connectome helped to create a wiring diagram for several cortical regions and thalamic nuclei (Hunnicutt et al, 2014; Oh et al, 2014). …”

Optogenetics: 10 years of microbial opsins in neuroscience

“…Many studies have employed optogenetics to discover and map the pathways along which such information flows in the brain, including analysis of physical circuit connectivity itself 84,85 , tagging cells defined by type or connectivity for use in other analyses 86 , and integrating with fMRI or PET imaging to generate brain-wide maps of activity patterns recruited by defined neural cells or projections 87,88 . Optogenetic methods have also yielded insight into the dynamics of information transmission in neural circuits more generally—for example, regarding the modulation of activity by oscillatory rhythms 41,89–97 , the causal significance of phase timing within the theta rhythm 98 , the influence of gamma rhythmicity on information propagation 41,89,90 and (dovetailing with parallel insights from genetic interventions 99,100 ) the real-time regulation of information flow via the dynamic balance of excitation and inhibition 90,101–110 .…”