Dendrites can help neurons perform complex calculations

In the human brain, neurons perform complex calculations on the information they receive

The researchers found that within a single neuron, different types of dendrites receive input from different parts of the brain and process it differently

In the neurons the researchers examined in this study, this dendritic processing appears to help cells take in visual information and combine it with motor feedback, a circuit involved in navigation and motor planning

"Our hypothesis is that these neurons have the ability to pick out specific features and landmarks in the visual environment and combine them with information such as running speed, where I'm going, when to start, etc.

complex calculation

Any given neuron can have dozens of dendrites, which receive synaptic input from other neurons

Previous research has shown that dendrites can amplify incoming signals through specialized proteins called NMDA receptors

This phenomenon, known as superlinearity, is thought to help neurons distinguish between inputs that are closer or farther apart in time or space, Harnett said

In the new study, the MIT researchers wanted to determine whether different types of input target different types of dendrites, and if so, how that would affect the computations these neurons perform

Harnett and his colleagues chose a part of the brain called the retrosplenial cortex (RSC) for their study because it is a good model for the correlative cortex

In a study in mice, the researchers first showed that three different types of input enter the pyramidal neurons of the RSC: from the basal dendrites of the visual cortex, from the apical oblique dendrites of the motor cortex, from the lateral nucleus of the thalamus, from the visual processing area , clustered dendrites

"Until now, there hasn't been a lot of mapping of which inputs go into these dendrites," Harnett said

a series of reactions

The researchers then measured the electrical activity in each compartment

On the basal dendrites, the researchers saw what they expected: Input from the visual cortex stimulated ultralinear electrical spikes produced by NMDA receptors

"It was shocking because no one had ever reported it before," Harnett said

These linear inputs may represent information such as running speed or destination, while visual information entering the basal dendrites represents landmarks or other features of the environment, Harnett said

In clustered dendrites that receive thalamic input, NMDA spikes appear to be generated, but not easily