Recurrent excitation and inhibition in the optical zone of the cortex

We analyzed the slow negative wave appearing in the optic cortex of the rabbit after a single afferent irritation and the specific "enhancing" response developing after subsequent repeated stimulations of the subcortical white matter. The first type of reaction is accompanied by recurrent inhibition of cortical neurons, the second by recurrent excitation. It is assumed that the optic cortex contains well developed both excitatory and inhibitory recurrent links.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 418–422, July–August, 1970.     

The recovery of the reactivity of the auditory system in the dolphin Tursiops truncatus to paired acoustic stimuli with different spectra]

Recovery cycles of the auditory brainstem responses were studied in the bottle-nosed dolphin, Tursiops truncatus, using paired acoustic clicks. The recovery time was longer if both clicks had identical spectra (50% recovery at 0.9 ms), as compared with that of different spectra (50% recovery at 0.35 ms). These results can explain a different recovery time of evoked responses after an artificial sound and after own locating one.     

Color sensitivity in the receptive fields of neurons of the squirrel visual cortex

Color-opponent properties in neurons of the primary visual cortex were investigated in the squirrel. All neurons responded to the presentation of both black and white visual stimuli and of colored stimuli — mainly to blue and green. In 65% of test neurons a response only occurred when blue and green stimuli were applied while the remaining cells partially responded to red. Neurons were divided into groups according to how they responded to the presentation of stimuli composed of black and white: whether nonselective, directionally selective, or orientationally selective (simple or complex). No color-opponent properties were found in any of these groups at receptive field level. The whole or parts of the receptive field responded similarly to the presentation of white, blue, or green stimuli of the same shape. The way in which the receptive fields were divided into on- and off-regions and between directional and orientational selectivity does not depend on the color of the visual stimuli. Findings are discussed with regard to the presence of opponent-color cells in squirrel retina and lateral geniculate body.A. N. Severtsov Institute of Evolutionary Morphology and Animal Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 764–770, November–December, 1985.     

Rabbit visual cortical neurons with simple and complex receptive fields

Receptive fields of neurons of the rabbit visual cortex selective for stimulus orientation were investigated. These receptive fields were less well differentiated than those of the analogous neurons of the cat visual cortex (large in size and circular in shape). Two mechanisms of selectivity for stimulus orientation were observed: inhibition between on and off zones of the receptive field (sample type) and oriented lateral inhibition within the same zone of the receptive field (complex type). Lateral inhibition within the same zone of the receptive field also took place in unselective neurons; "complex" selective neurons differed from them in the orientation of this inhibition. A combination of both mechanisms was possible in the receptive field of the same neuron. It is suggested that both simple and complex receptive fields are derivatives of unselective receptive fields and that "complex" neurons are not the basis for a higher level of analysis of visual information than in "simple" neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 13–21, January–February, 1978.     

Frequency tuning curves of the dolphin's hearing: envelope-following response study

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in dolphins (Turslops truncatus). The EFR was evoked by amplitude-modulated probes of various frequencies. A modulation rate of 600 Hz was found to fit the requirement to have a narrow spectrum and evoke EFR of large amplitude. Tuning curves were obtained within the frequency range from 11.2 to 110 kHz. The Q₁₀ values of the obtained tuning curves varied from 12–14 at the 11.2 kHz center frequency to 17–20 at the 64–90 kHz frequencies.Abbreviations ABR auditory brainstem response - EFR envelope following response - ERB equivalent rectangular bandwidth     

ABR frequency tuning curves in dolphins

Tone-tone masking was used to determine auditory brain-stem response tuning curves in dolphins (Tursiops truncatus) in a simultaneous-masking paradigm. The Q ₁₀ of the curves was as large as 16–19 in the frequency range 64–128 kHz. In the range 45–16 kHz, Q ₁₀ decreased proportionally to the frequency with the bandwidth of the curves being constant, about 3.5–4 kHz at the 10-dB level. Tuning curves below 45 kHz are supposed to reflect broad spectral bandwidth of the probe's effective part which is no longer than 0.5 ms, irrespective of actual probe duration. Tuning curves above 64 kHz are supposed to reflect the real frequency tuning of the dolphin's auditory system.Abbreviations ABR auditory brain stem response - AP action potential