Prenatal activity from thalamic neurons governs the emergence of functional cortical maps in mice

Brain map of touch sensation The brain's somatosensory cortex contains a topographical map that reflects touch sensation inputs. During embryonic development, axons from the midbrain thalamus build columnar connections to the cortex in the absence of sensory input. Working in mice, Antón-Bolaños et al. found that these thalamocortical connections are responsible for organizing the somatosensory cortex (see the Perspective by Tiriac and Feller). Organization of the map in the cortex depends on spontaneous calcium waves in the embryonic thalamus. Thus, the somatosensory map is sketched out before actual sensory input begins to refine the details. Science, this issue p. 987; see also p. 933 Mapping of touch sensation into brain regions is driven prenatally by spontaneous brain activity. The mammalian brain’s somatosensory cortex is a topographic map of the body’s sensory experience. In mice, cortical barrels reflect whisker input. We asked whether these cortical structures require sensory input to develop or are driven by intrinsic activity. Thalamocortical columns, connecting the thalamus to the cortex, emerge before sensory input and concur with calcium waves in the embryonic thalamus. We show that the columnar organization of the thalamocortical somatotopic map exists in the mouse embryo before sensory input, thus linking spontaneous embryonic thalamic activity to somatosensory map formation. Without thalamic calcium waves, cortical circuits become hyperexcitable, columnar and barrel organization does not emerge, and the somatosensory map lacks anatomical and functional structure. Thus, a self-organized protomap in the embryonic thalamus drives the functional assembly of murine thalamocortical sensory circuits.