TY - JOUR
T1 - Response properties of visual neurons in the turtle nucleus isthmi
AU - Saha, Debajit
AU - Morton, David
AU - Ariel, Michael
AU - Wessel, Ralf
N1 - Funding Information:
pathway. Large-field neurons in the SGC layer of the turtle tectum project to the nucleus rotundus in a non-topographic manner, forming a key element of tectofugal pathway (Reiner 1994; Belekova et al. 2003). The tectal SGC neurons’ dendritic branches extend into the superficial reti-norecipient tectal layers (SFGS). The topographically organized columnar Ipc axon terminals spatially overlap with the RGC axons and the SGC dendrites. Thus, the release of ACh from Ipc axon terminals across several tectal layers provides ample potential for a spatially specific cholinergic modulation of retino-tectal synaptic transmission and in turn, the ascending visual pathway. This conjecture is supported by the observations that isthmic activity enhances calcium influx into the optic nerve fiber terminals in frog (Dudkin and Gruberg 2003) and by
PY - 2011/2
Y1 - 2011/2
N2 - The optic tectum holds a central position in the tectofugal pathway of non-mammalian species and is reciprocally connected with the nucleus isthmi. Here, we recorded from individual nucleus isthmi pars parvocellularis (Ipc) neurons in the turtle eye-attached whole-brain preparation in response to a range of computer-generated visual stimuli. Ipc neurons responded to a variety of moving or flashing stimuli as long as those stimuli were small. When mapped with a moving spot, the excitatory receptive field was of circular Gaussian shape with an average half-width of less than 3°. We found no evidence for directional sensitivity. For moving spots of varying sizes, the measured Ipc response-size profile was reproduced by the linear Difference-of-Gaussian model, which is consistent with the superposition of a narrow excitatory center and an inhibitory surround. Intracellular Ipc recordings revealed a strong inhibitory connection from the nucleus isthmi pars magnocellularis (Imc), which has the anatomical feature to provide a broad inhibitory projection. The recorded Ipc response properties, together with the modulatory role of the Ipc in tectal visual processing, suggest that the columns of Ipc axon terminals in turtle optic tectum bias tectal visual responses to small dark changing features in visual scenes.
AB - The optic tectum holds a central position in the tectofugal pathway of non-mammalian species and is reciprocally connected with the nucleus isthmi. Here, we recorded from individual nucleus isthmi pars parvocellularis (Ipc) neurons in the turtle eye-attached whole-brain preparation in response to a range of computer-generated visual stimuli. Ipc neurons responded to a variety of moving or flashing stimuli as long as those stimuli were small. When mapped with a moving spot, the excitatory receptive field was of circular Gaussian shape with an average half-width of less than 3°. We found no evidence for directional sensitivity. For moving spots of varying sizes, the measured Ipc response-size profile was reproduced by the linear Difference-of-Gaussian model, which is consistent with the superposition of a narrow excitatory center and an inhibitory surround. Intracellular Ipc recordings revealed a strong inhibitory connection from the nucleus isthmi pars magnocellularis (Imc), which has the anatomical feature to provide a broad inhibitory projection. The recorded Ipc response properties, together with the modulatory role of the Ipc in tectal visual processing, suggest that the columns of Ipc axon terminals in turtle optic tectum bias tectal visual responses to small dark changing features in visual scenes.
KW - GABAergic inhibition
KW - Nucleus isthmi
KW - Receptive field
KW - Tectum
KW - Vision
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U2 - 10.1007/s00359-010-0596-3
DO - 10.1007/s00359-010-0596-3
M3 - Article
C2 - 20967450
AN - SCOPUS:78751638460
SN - 0340-7594
VL - 197
SP - 153
EP - 165
JO - Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology
JF - Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology
IS - 2
ER -