Noise or Spontaneous Activity in Neuronal Systems, Causes and Strategies
Joby Joseph, Center for Neural and Cognitive Systems, University of Hyderabad
Neurons in the different regions of the brain are seen to have spontaneous activity. Some of this are attributed to endogenously generated desirable activity of the system (for example pacemakers and activities during memory consolidation), some related to short term memories, while some of the activities are considered to be noise in the system. Some of this noise may be because of the unreliable mechanisms at synaptic and transduction machinery or at the cell membranes of neurons in the organism. Organism has evolved different strategies to perform in these noisy conditions.
In the olfactory pathway in insect systems it is observed that in the sensory neurons and the second order neurons (called projection neurons) to which all the receptor neurons of same type converge, have relatively high levels of spontaneous activity. However the third order neurons (Kenyon cells) that these converge to are eerily silent and yet sensitive to odors at very low concentrations. Is the spontaneous activity in the second order neuron caused by the receptor neurons? Why is it not silent though there is convergence to it from all the receptor neurons of identical types? How is it that the third order neurons maintain very low spontaneous activity while they are able to respond stably to odors ranging from very low to very high concentrations?