Summation (neurophysiology) - Current Research

Current Research

The microelectrodes used by Katz and his contemporaries pale in comparison to the technologically advanced recording techniques available today. Spatial summation began to receive a lot of research attention when techniques were developed that allowed the simultaneous recording of multiple loci on a dendritic tree. A lot of experiments involve the use of sensory neurons, especially optical neurons, because they are constantly incorporating a ranging frequency of both inhibitory and excitatory inputs. Modern studies of neural summation focus on the attenuation of postsynaptic potentials on the dendrites and the cell body of a neuron. These interactions are said to be nonlinear, because the response is less than the sum of the individual responses. Sometimes this can be due to a phenomenon caused by inhibition called shunting, which is the decreased conductance of excitatory postsynaptic potentials.

Shunting inhibition is exhibited in the work of Michael Ariel and Naoki Ago, who experimented with whole cell recording on the turtle basal optic nucleus. Their work showed that spatial summation of excitatory and inhibitory postsynaptic potentials caused attenuation of the excitatory response during the inhibitory response most of the time. They also noted a temporary augmentation of the excitatory response occurring after the attenuation. As a control they tested for attenuation when voltage-sensitive channels were activated by a hyperpolarization current. They concluded that attenuation is not caused by hyperpolarization but by an opening of synaptic receptor channels causing conductance variations.