Until recently, scientists believed that dendrites were passive in nature and could only propagate electrical signals. However, it has recently come to light that dendritic activity strongly influences somatic action potentials. Scientists of the DENDRITE2BEHAVIOR (From dendrite to behavior: fiberoptic imaging and optogenetic manipulation of dendritic activity in behaving animals) project optically manipulated a selected region in the dendrites of the cortical layer pyramidal neurons in the brain. Their goal was to modulate animal behaviour. Researchers developed an extremely lightweight fibre-optic micro-periscope system for selective photostimulation of the rodent cortex in freely behaving animals. This breakthrough helped them produce research outputs of high significance that will be shortly submitted for publication in the form of four journal articles. Project members initially focussed on the influence of dendritic activity on electroencephalogram (EEG) signals. They conclusively demonstrated that the dendrites of cortical layer 5 (L5) pyramidal neurons produce calcium spikes with an amplitude as large as excitatory postsynaptic potentials. These spikes also strongly influence the potential measured at the cortical surface. These results challenge the current assumption that EEG signals reflect the excitatory postsynaptic activity. EEG is widely used for clinical and non-clinical applications, and project data could be instrumental in changing EEG data interpretation for healthy and diseased individuals. Notable is the development of a novel method involving the simultaneous use of two micro-periscope systems that enable researchers to activate two separate cortical layers in vivo. L5 pyramidal neurons extend their dendrites into all cortical layers (L1 to L6). A technical first, researchers could now study the association of top-down signals at L1 with sensory, bottom-up signals at L4. As a result, researchers provided the first in vivo evidence that L5 pyramidal neurons are extremely sensitive to coincidentally arriving inputs at different cortical layers. Project outcomes are highly significant in the neuroscience arena. The cerebral cortex is linked to major cognitive functions such as attention, memory, perception, and language. Researchers can now add to their arsenal a powerful tool that permits them to selectively and accurately activate different cortical layers in vivo. This has huge implications for detecting and resolving neurological and behavioural disorders.
Dendrite, cerebral cortex, behaviour, optogenetic, pyramidal neuron, micro-periscope, EEG, neurological disorder