Abstract
A major challenge in current neuroscience is to understand the concerted functioning of distinct neurons involved in a particular behavior. This goal first requires achieving an adequate characterization of the behavior as well as an identification of the key neuronal elements associated with that action. Such conditions have been considerably attained for the escape response to visual stimuli in the crab Neohelice. During the last two decades a combination of in vivo intracellular recordings and staining with behavioral experiments and modeling, led us to postulate that a microcircuit formed by four classes of identified lobula giant (LG) neurons operates as a decision-making node for several important visually-guided components of the crab’s escape behavior. However, these studies were done by recording LG neurons individually. To investigate the combined operations performed by the group of LG neurons, we began to use multielectrode recordings. Here we describe the methodology and show results of simultaneously recorded activity from different lobula elements. The different LG classes can be distinguished by their differential responses to particular visual stimuli. By comparing the response profiles of extracellular recorded units with intracellular recorded responses to the same stimuli, two of the four LG classes could be faithfully recognized. Additionally, we recorded units with stimulus preferences different from those exhibited by the LG neurons. Among these, we found units sensitive to optic flow with marked directional preference. Units classified within a single group according to their response profiles exhibited similar spike waveforms and similar auto-correlograms, but which, on the other hand, differed from those of groups with different response profiles. Additionally, cross-correlograms revealed excitatory as well as inhibitory relationships between recognizable units. Thus, the extracellular multielectrode methodology allowed us to stably record from previously identified neurons as well as from undescribed elements of the brain of the crab. Moreover, simultaneous multiunit recording allowed beginning to disclose the connections between central elements of the visual circuits. This work provides an entry point into studying the neural networks underlying the control of visually guided behaviors in the crab brain.
Highlights
To fulfill its biological function the escape response to an impending threat needs to be executed quickly. This implies that sensory information about danger stimuli must be transformed into avoidance actions with the shortest delay, a purpose that is favorably achieved by large neurons capable of conveying information in terms of action potentials (Herberholz and Marquart, 2012)
The distribution of interspike intervals (ISIs) depicted in Figure 1J confirms that none of the units reflect refractory period violations (i.e., ISI < 1–2 ms)
We have identified units that responded as lobula complex directional cells (LCDC) neurons
Summary
To fulfill its biological function the escape response to an impending threat needs to be executed quickly This implies that sensory information about danger stimuli must be transformed into avoidance actions with the shortest delay, a purpose that is favorably achieved by large neurons capable of conveying information in terms of action potentials (Herberholz and Marquart, 2012). The extracellular recording is more performed and can be maintained for hours, but only brings information about action potential activity, without direct knowledge of which neuron originated the recorded spike firing. These two techniques bring about complementary information
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