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 Coherent Activity in Vertebrate Brains
Action Potential Signals

Coherent Activity in Vertebrate Brains

Population Signals
When a low magnification objective is used to form an image of a vertebrate preparation on the 464 element photodiode array or 80x80 pixel CCD camera, each pixel receives light from hundreds or thousands of neurons. Now, the signals are the population average of the membrane potential or calcium concentration changes in those neurons. These population signals monitor coherent activity, i.e. those events that involve simultaneous changes in activity of a (substantial) fraction of the neurons in the imaged region.

Two examples are illustrated. First, maps of the glomeruli that are activated by odor stimuli to the nose. And, second, the oscillations in the olfactory bulb elicited by odorants.

Odorant elicited activity in the turtle and mouse olfactory bulbs
 Figure 1. Calcium signals - turtleWe made maps of the input to the olfactory bulb. We stained the olfactory receptor neurons in the nose with Calcium Green - dextran and waited for several days to allow the dye to be transported to the receptor nerve terminals in the olfactory bulb. In in vivo measurements we applied odorant stimuli to the nose and measured the changes in calcium concentration in the receptor neuron nerve terminals in the olfactory bulb glomeruli.

Turtle.
 The traces at the bottom of Figure 1 show the time course of the responses to two odorants, cineole and hexanone, from three locations on the turtle olfactory bulb. While the time courses of the response are the same everywhere in the bulb and the same for both odorants, the size of the response from the three areas were different for the two odorants. We characterized the response by measuring the signal amplitude and making the pseudo-color plots of amplitude versus position shown in the top two frames. Red is the largest signal and purple is no detected signal. Clearly, the maps of activity for the two odorants are quite different and thus such maps could be used for odor recognition.

What happens when the odorant concentration is changed? The results in Figure 2 show the maps for two odorants at three different concentrations. The top row is isoamyl acetate and the bottom is cineole. Again, the maps of activity are different for the two odorants. In addition, the maps remain consistently different over this substantial concentration range. Thus, the turtle could recognize odorants in a concentration invariant way just by reading the maps of input. Others have speculated that piriform cortex is organized as an association cortex and thus could have the role of map reader.

Figure 2. Calcium signals - turtle

Mouse. 
 The results of similar experiments in the mouse are different. In the mouse the maps change with odorant concentration; more glomeruli are activated with increasing concentration. Figure 3 shows (now using a gray scale) the responses to two concentrations of two odorants, hexanone and butanone. The left panels show that at the low concentration the odorants activated only a small number of glomeruli. At the high concentration (right panels) the odorants activated many more glomeruli. Thus, the maps in the mouse are not concentration invariant at the level of the input to the bulb. Perhaps further processing is needed to generate concentration invariance.
Future plans.
  1. We will attempt to achieve specific labeling of the mitral neurons, the output neurons of the bulb. Comparison of the maps of input and output would make an important contribution to understanding the functional role of the olfactory bulb.

  2. We hope to use the ability to specifically monitor the input to the olfactory bulb to ask what role presynaptic inhibition plays in sculpting that input.

 

 Figure 3. Calcium signals - mouse

Odorant elicited oscillations in the turtle olfactory bulb.
It has long (>60 years) been known from local field potential electrode measurements that odorants elicit oscillations in the olfactory bulb. Using voltage sensitive dye imaging we found that in fact odorants elicit three different oscillations in the turtle. Figure 4 shows the response from seven different detectors from different regions of the turtle olfactory bulb. In the rostral area there is a large, relatively fast and long lasting oscillation, in the middle region there is a small and short latency oscillation, and in the caudal region there is a low frequency oscillation. Although the number of odorants we have tested is small, as far as we can tell these oscillations are the same for all odorants and are thus unlikely to be used for odorant recognition. However, preliminary experiments suggest that the oscillations are strikingly dependent on the history of odorant presentation. The response to a second odorant stimulus delivered several seconds after the first is markedly altered.

  Figure 4. Voltage signals - turtle

Future plans.
  1. First, we will characterize the changes in the three osciallations that occur on repeated odorant presentations. Second, we will look for effects of inserting a new odorant in the stimulus train.

  2. We plan to carry out similar experiments on the mouse olfactory bulb. The mouse is very interesting because some of the methods for specifically staining mitral neurons depend on the use of transgenic animals.

References

Wuskell, J.P., Wei, M-w., Boudreaux, D., Jin, L., Engl, R., Chebolu, R., Bullen, A., Hoffacker, K.D., Kerimo, J., Cohen, L.B., Zochowski, M.R., and Loew, L.M. (2006) Synthesis, spectra, delivery and potentiometric responses of new styryl dyes with extended spectral ranges.  J. Neuroscience Methods, 151: 200-215.

Eugenin, J., Nicholls, J. G., Cohen, L.B., and Muller K., (2005) Optical recording from respiratory pattern generator of foetal mouse brainstem reveals a distributed network. Neuroscience, 137:  1221-1227..

Spors, H., Wachowiak, M., Cohen, L.B., and Friedrich, R.W. (2006) Temporal dynamics and latency patterns of receptor neuron input to the olfactory bulb. J. Neuroscience, 26:  1247-1259.

Vucinic, D., Cohen, L.B., and Kosmidis, E.K. (2006) Presynaptic centre-surround inhibition shapes odorant evoked input to the mouse olfactory bulb in vivo. J. Neurophysiology, (2006)  95:1881-1887.

Baker, B.J., Lee, H., Pieribone, V.A., Cohen, L.B., Isacoff, E.Y., Knopfel, T., Kosmidis, E.K. (2007) Three flourescent protein voltage sensors exhibit low plasma membrane expression in mammalian cells.  J. Neuroscience Methods, 161: 32-38.

Dimitrov, D., He, Y., Mutoh, H., Baker, B.J., Cohen, L.B., Akemann, W., and Knopfel, T. (2007) Engineering and characterization of an enhanced fluorescent protein voltage sensor.  PLOS One, 2(5): e440.


Zochowski, M. R., and  Cohen, L. B. (2005), Oscillations in the olfactory bulb carry information about the history of odorant presentation. J.Neurophysiology, 94: 2667-2675.

Wachowiak, M, and Cohen, L.B. (2003) Correspondence between odorant-evoked patterns of receptor neuron input and intrinsic optical signals in the mouse olfactory bulb. J. Neurophysiology, 89: 1623-1639.

Ying-wan Lam, Lawrence B. Cohen, and Michal R. Zochowski (2003) Effect of  odorant quality on the three oscillations and the DC signal in the turtle olfactory bulb. European J. Neuroscience, 17: 436-446.

Wachowiak M, Cohen LB, and Zochowski, M. R. (2002) Distributed and concentration invariant spatial representations of odorants by receptor neuron input to the turtle olfactory bulb. J. Neurophysiology, 87: 1035-1045.

Wachowiak, M. and Cohen, L.B. (2001) Representation of odorants by receptor neuron input to the mouse olfactory bulb. Neuron,  32: 723-735.

Ying-wan Lam, Lawrence B. Cohen, Matt Wachowiak, and Michal R. Zochowski (2000) Odors elicit three different oscillations in the turtle olfactory bulb. J. Neuroscience, 20:749-762.

Wachowiak, M., Zochowski, M., Cohen, L.B., and Falk, C. X. (2000) The spatial representation of odors by olfactory receptor neuron input to the olfactory bulb is concentration invariant. Biological Bulletin, 199: 162-163.

Wachowiak, M. and Cohen, L.B. (1998) Presynaptic afferent inhibition of lobster olfactory receptor cells: Reduced action potentialpropagation into axon terminals. J. Neurophysiology, 80, 1011-1015.

Ying-wan Lam, Lawrence B. Cohen, Matt Wachowiak, and Michal R.Zochowski (2000) Odors elicit three different oscillations in the turtle olfactory bulb. J. Neuroscience, 20:749-762.

Wachowiak, M., and Cohen, L. B. (1999) Presynaptic inhibition of primary olfactory afferents mediated by different mechanisms in the lobster and turtle. J. Neuroscience, 19, 8808­8817.

Prechtl, J.C., L.B. Cohen, B. Pesaran, P.P. Mitra, and D. Kleinfeld (1997) Visual stimuli induce propagating waves of electrical activity in the turtle cortex. ,Proc Nat Acad Sci (USA), 94, 7621-7626.

London, J.A., L.B. Cohen, and J.Y. Wu (1989) The spread of epileptiform discharges in the somatosensory cortex of the rat measured with voltage sensitive dyes. J Neuroscience, 9, 2182-2190.

Kauer, J.S., D.M. Senseman, and L.B. Cohen (1987) Odor elicited activity monitored simultaneously from 124 regions of the salamander olfactory bulb using a voltage sensitive dye. Brain Res,, 418, 255-261.

Orbach, H.S., L.B. Cohen, and A. Grinvald (1985) Optical mapping of electrical activity in rat somatosensory and visual cortex. J Neuroscience, 5, 1886-1895. 

 

Last Updated 11.02.09 3:22 PM (cla)

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