Object approach computation by a giant neuron and its relation with the speed of escape in the crab Neohelice

DAMIAN OLIVA; DANIEL TOMSIC

JOURNAL OF EXPERIMENTAL BIOLOGY

COMPANY OF BIOLOGISTS LTD

Lugar: Cambridge; Año: 2016 vol. 219 p. 3339 - 3352

0022-0949

Upon detection of an approaching objectthe crab Neohelice granulata continuously regulates thedirection and speed of escape according to ongoing visual information. Thesevisuomotor transformations are thought to be largely accounted for by a smallnumber of motion-sensitive giant neurons projecting from the lobula (thirdoptic neuropil) towards the supraesophageal ganglion. One of these elements,the monostratified lobula giant neurons of type 2 (MLG2), proved to be highlysensitive to looming stimuli (a 2D representation of an object approach). By performing in vivo intracellularrecordings we assessed the response of the MLG2 neuron to a variety of loomingstimuli representing objects of different sizes and velocities ofapproach. This allowed us: a) to identify some of the physiologicalmechanisms involved in the regulation of the MLG2 activity and to test asimplified biophysical model of its response to looming stimuli; b) to identifythe stimulus optical parameters encoded by the MLG2, and to formulate aphenomenological model able to predict the temporal course of the neural firingresponses to all looming stimuli; c) to incorporate the MLG2 encodedinformation of the stimulus (in terms of firing rate) into a mathematical modelable to fit the speed of the escape run of the animal. The agreement betweenthe model predictions and the actual escape speed measured on a treadmill forall tested stimuli strengthens our interpretation of the computations performedby the MLG2 and of the involvement of this neuron in the regulation of theanimal´s speed of run while escaping from approaching objects.