Planning and Executing Movement at a Neuronal Level

Researchers at Karolinska Institutet have mapped how different neurons process information to plan and execute our movements at the right time and intensity. The results, published today in Cell Reports, show that different cell types in the striatum receive signals from completely different parts of the cerebral cortex and thus respond to different types of information.

Many behaviors occur in response to sensory input from our environment. For example, when playing a new piece on the piano, we adjust our finger movements according to the sound we hear and the sensory feedback from the keys. The team investigated how this works by studying the neuronal network that allows us to align our planned movements to sensory information. The neurons that underlie this function are in the striatum, which is part of the basal ganglia.

While playing piano, sensory feedback from our fingertips is processed in the somatosensory cortex, and movements are planned in the motor cortex. Information from the somatosensory cortex, the motor cortex, and other brain areas such as the thalamus are sent to the striatum, where movement plans and sensory information are first combined. Based on the broad information delivered by these inputs, the striatum is able to generate a precisely timed output signal that is sent back to the muscles and allows us to press the next keys correctly on the piano.

“Although it has long been known that the striatum is composed of different types of nerve cells, it is unclear how striatal cells achieve this complex function,” says first author Yvonne Johansson. “To address this question, we asked which striatal cell populations process which incoming information.”

The researchers used optogenetics, among other technologies, to analyze which of five important cell types in the striatum are responsible for the communication from the motor cortex, the somatosensory cortex, and the thalamus.

Studies on mice revealed that striatal medium spiny neurons strongly respond to sensory inputs representing a sensation of touch. Another class of striatal neurons, the low-threshold spiking interneurons, hardly respond to inputs carrying sensory information but are strongly activated by inputs from motor cortex. In contrast, cholinergic interneurons respond most strongly to thalamic inputs, which are thought to notify us that something important is happening in our environment.

The researchers also found that the responses of the different neuron classes are mediated by different receptor compositions. As some receptors open faster than others, the receptors strongly shape the timing of the response.