Final Article Summary
Precise Firing Events Are Conserved across Neurons
Pamela Reinagel and R. Clay Reid
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
The Journal of Neuroscience, August 15, 2002, 22(16):6837–6841

Right now as you read this article summary your eyes are picking up visuals that your brain is processing. More specifically photons are striking photoreceptor cells in your retina and exciting a signal transduction pathway involving opsin proteins. This excitation eventually leads to a series of action potentials that travel through the optic nerves and 90% of this signal will converge in a part of the thalamus called the lateral geniculate nucleus (LGN). The LGN orders the axon sequences from both eyes and helps create a 3-dimesional spatial visual when it sends a single output to the visual cortex for further processing. Since the action potential of neurons are consistent the only way the LGN cells end up relaying this information is in a precise temporal pattern. In previous papers it is shown that this pattern can be reproduced in a specific cell. In this article they discover that not only is this specific temporal pattern a trait for every LGN cell in a specific animal, yet it is in fact a pattern even for different animals and classes of LGN cells. The methodology Reinagel and Reid used to conduct this experiment was established in many papers they previously wrote. They observed individual LGN neurons in four different animals who were anesthetized at the time. They classified the cells by using spatiotemporal receptive field mapping. For this experiment they only used temporal X cells, which are cells that modulate frequencies one fourth a cycle away from the their respective peak action response. They subjected these different animal LGN cells to a random diffuse flicker, a flicker of a certain luminance emitted at in a random sequence with a controlled frequency. They did 128 trials for each cell type and recorded the data on a peristimulus time histogram (PSTH) which plots the probability of firing an action versus time. After normalizing data and removing small latency differences that exist between cell types they produced really interesting results.

The first thing they observed from four different animals and 7 different cells (from each animal) is that regardless of cell class or animal the cell seemed to fire action potentials around the same time. In addition using Gaussian statistics applied to the PSTH they found that the average action time (width) ranged between 1-4msec. Using this data, they then compared the difference between different cell actions with the averages of the action’s width only to uncover that the majority of the action times differed by less than the average width of that respected action (refer to plot). In the plot if