Commissural channels of visual information transmission

Experiments were made in adult cats with different transections of the classical and commissural visual tracts to study evoked potentials and unit neuronal activity in response to visual stimulation. The commissural channels of the telencephalon, diencephalon and mesencephalon were demonstrated to be highly effective in visual information conduction to the visual cortex. Complete transection of the classical and commissural tracts with the exception of the commissural tract of the third ventricle fundus and midbrain reticular formation resulted in the disappearance of evoked potentials in the visual cortex in response to light flashes, despite the fact that 8 of the 15 recorded neurons responded to photostimulation. Activation of such neurons was caused by visual information conduction via two possible commissural channels: midbrain reticular formation and subventricular interhemispheric commissures of the diencephalon.     

Extracallosal channels of interhemispheric transmission of visual information

Evoked potentials (EP) in response to light flashes were recorded in cats with different degree of optical tract disconnection. In intact and operated on animals, the latent period of the first component of these EP was the same as in the visual cortex. The different degree of disconnection of the classic and commissural optical tract brought about an increase in the amplitude of commissural potentials. The data obtained point to the existence of the effective callosal and extracallosal volleys of interhemispheric transmission of visual information, which are also likely to pay an essential part in compensatory processes of the optical system.     

Interhemispheric transmission of visual information: behavioral and electrophysiologic aspects

Efficiency of callosal and extracallosal channels of interhemispheric transfer of visual information was studied by behavioural and electrophysiological methods on cats with sections of classical and commissural pathways of the visual system. The results showed a high ability of the operated animals to form conditioned defensive reflex to visual stimuli. The primary complexes of evoked potentials to light flashes in the projection cortex of both hemispheres were also preserved. The data show the significant role of the callosal and extracallosal pathways of the transmission of visual information across the midline.     

Pathways for transmission of visual and auditory information to the cat caudate nucleus

Visual and auditory projections to the cat caudate nucleus were investigated using the horseradish peroxidase retrograde axonal transport technique in conjunction with that of experimental degeneration of retinal axons. It was found that visual information may reach the caudate nucleus not just through well-known polysynaptic pathways from the cerebral cortex but also following oligosynaptic (transpulvinar, lateroposterior nucleus, suprageniculate nucleus, and nucleus limitans of the thalamus) as well as bisynaptic pathways (via the medial and lateral terminal nuclei of the accessory optical tract, pulvinar, pretectum, intermediary layer of the superior colliculus, and the supraoptic nucleus); some of these pathways were identified for the first time. Direct retinal inputs were found in the suprageniculate nucleus. Additional structures were discovered through which auditory information may reach the caudate nucleus, i.e., the dorsal nucleus of the parvocellular portion of the lateral geniculate body, the deep-lying superior colliculus, and the dorsal and ventral nuclei of the lateral lemniscus. The physiological significance of the pathways described for possible transmission of visual and auditory impulses is discussed and a new principle underlining the organization of sensory inputs into the caudate nucleus is put forward.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 512–520, July–August, 1987.     

Pathways for the transmission of visual information in the protocerebrum of the drone fly Eristalis tenax]

Studies have been made on the structure of neuropiles and visual pathoways in the brain of the fly E. tenax L. (Diptera, Syrphidae). The retina is projected on laminar structures in the visual ganglia only; other protocerebrum neuropiles lack this projection. All the comissures connecting contralateral visual ganglia, consist of several hundreds of fibers, whereas the binocular zone of both eyes includes more than 4,000 ommatidia. Neither the visual ganglia, nor other protocerebrum neuropiles may serve as a substrate for topographic imposition of projections of the corresponding parts in both retines. The mechanism of binocular interaction in insects presumably differs from that in mammals (primates, carnovores).     

The transmission sense of information

Biologists rely heavily on the language of information, coding, and transmission that is commonplace in the field of information theory developed by Claude Shannon, but there is open debate about whether such language is anything more than facile metaphor. Philosophers of biology have argued that when biologists talk about information in genes and in evolution, they are not talking about the sort of information that Shannon’s theory addresses. First, philosophers have suggested that Shannon’s theory is only useful for developing a shallow notion of correlation, the so-called “causal sense” of information. Second, they typically argue that in genetics and evolutionary biology, information language is used in a “semantic sense,” whereas semantics are deliberately omitted from Shannon’s theory. Neither critique is well-founded. Here we propose an alternative to the causal and semantic senses of information: a transmission sense of information, in which an object X conveys information if the function of X is to reduce, by virtue of its sequence properties, uncertainty on the part of an agent who observes X. The transmission sense not only captures much of what biologists intend when they talk about information in genes, but also brings Shannon’s theory back to the fore. By taking the viewpoint of a communications engineer and focusing on the decision problem of how information is to be packaged for transport, this approach resolves several problems that have plagued the information concept in biology, and highlights a number of important features of the way that information is encoded, stored, and transmitted as genetic sequence.     

Cellular noise and information transmission

1. Download : Download high-res image (90KB)
2. Download : Download full-size image

     

Adaptive rescaling maximizes information transmission

Adaptation is a widespread phenomenon in nervous systems, providing flexibility to function under varying external conditions. Here, we relate an adaptive property of a sensory system directly to its function as a carrier of information about input signals. We show that the input/output relation of a sensory system in a dynamic environment changes with the statistical properties of the environment. Specifically, when the dynamic range of inputs changes, the input/output relation rescales so as to match the dynamic range of responses to that of the inputs. We give direct evidence that the scaling of the input/output relation is set to maximize information transmission for each distribution of signals. This adaptive behavior should be particularly useful in dealing with the intermittent statistics of natural signals.     

Propriospinal neurones as a relay system for transmission of cortico-spinal influences.

1. Synaptic organization and transmission have been studied in the lateral group of short propriospinal neurones of the lumbar and cervical regions of the cat spinal cord. Special attention was paid to their role in the transmission of cortico-spinal volleys. 2. The majority of these neurones are mono- or oligosynaptically excited after pyramidal tract stimulation. Convergence of excitatory actions from rubrospinal and lateral reticulospinal tracts was typical for these cells. Neurones with relatively low-level and delayed effects from segmental afferents are frequent in this population. 3. Temporal summation is important for the transmission of descending vlleys through these neurones. Mutual excitatory and recurrent inhibitory connections are supposed to play a substantial role in their function. 4. Possible participation of the short lateral propriospinal system in the transmission, transformation and re-distribution of corticofugal signals to the segmental spinal mechanisms is discussed.