Action Potential Signals

An array of 464 detectors is nearly optimal for detecting the individual action potentials in a preparations like the Aplysia abdominal ganglion which has about 1000 cell bodies. A very light touch to the siphon skin will elicit a gill withdrawal from an in vitro preparation. It also activates a very large number of neurons in the abdominal ganglion. Approximately half of this activity is illustrated in the figure where each line represents one neuron and each tic on the line represents one action potential. (From figure 2 of Wu et al, (1994)). The figure shows only half of the activity; thus the total number of abdominal ganglion neurons that respond to the light touch is about 250; the total number of neurons in all of Aplysia's central ganglia that respond is about 1,500. This number is surprisingly large. It had been claimed that the Aplysia gill-withdrawal reflex is both simple and well understood; our result makes that claim seem premature and causes one to consider the possibility that Aplysia's nervous system may function as a distributed system.

We have tried to determine the contribution that LE sensory neurons make to the motoneuron activity during gill-withdrawal reflex. Our results suggest that this contribution is about 5%; an order of magnitude less than the previous estimate of 58%.

We have also started experiments to see if the same kind of optical monitoring of spike activity can be done in a vertebrate nervous system. In measurements carried out with Mike O'Donovan and Pete Wenner, we have been able to specifically label small groups of neurons in an embryonic chick spinal cord with voltage-sensitive dyes. We are just on the edge of being able to detect the activity of individual neurons. This method could be useful.

As you can see from the reference list we haven't been active in this area in recent times.

Zochowski, M., L.B. Cohen, G. Fuhrmann, and D. Kleinfeld (2000), Distributed and partially separate pools of neurons are correlated with two different components of the gill withdrawal reflex in Aplysia.J. Neuroscience, 20: 8485-8492.

Hickie, C., L.B. Cohen, and P.M. Balaban (1997). LE sensory neurons make a minor contribution to the Aplysia gill­withdrawal reflex.Eur J Neurosci, 9, 627-636.

Wenner, P., Y. Tsau, L.B. Cohen, M.J. O'Donovan, and Y. Dan (1997). Voltage sensitive dye recording using retrogradely transported dye in the chicken spinal cord: staining and signal characteristics.J Neurosci Methods, 70, 111-120.

Tsau, Y., P. Wenner, M.J. O'Donovan, L.B. Cohen, L.M. Loew, and J.P. Wuskell (1997). Dye screening and signal­to­noise ratio for retrogradely transported voltage­sensitive dyes.J Neurosci Methods, 70, 121-129.

Hopp, H.P., C.X. Falk, L.B. Cohen, J.Y. Wu and A.I. Cohen (1996). Effect of feedback from peripheral movements on the neuron activity in the Aplysia abdominal ganglion.Eur J Neurosci, 8, 1865-1872.

Wu, J.Y., Y. Tsau, H.P. Hopp, L.B. Cohen, A.C. Tang, and C.X. Falk (1994). Consistency in nervous systems: Trial-to-trial and animal-to-animal variations in the response to repeated application of a sensory stimulus in Aplysia.J Neurosci, 14, 1366-1384.

Wu, J.Y., L.B. Cohen, and C.X. Falk (1994). Neuronal activity during different behaviors suggests a distributed neuronal organization in the Aplysia abdominal ganglion.Science, 263, 820-823.

Tsau, Y., J.Y. Wu, H.P. Hopp, L.B. Cohen, D. Schiminovich, and C.X. Falk (1994). Distributed aspects of the response to siphon touch in Aplysia: spread of stimulus information and cross correlation analysis.J Neurosci, 14, 4167-4184.

Falk, C.X., Wu Jy, L.B. Cohen, and C. Tang (1993). Non-uniform expression of habituation in the activity of distinct classes of neurons in the Aplysia abdominal ganglion.J Neurosci, 13, 4072-4081.

Zecevic, D., J.Y. Wu, L.B. Cohen, J.A. London, H.P. Hopp, and C.X. Falk (1989). Hundreds of neurons in the Aplysia abdominal ganglion are active during the gill-withdrawal reflex.J Neurosci, 9, 3681-3689.