Transmission Of Sensory Information Research Articles

Recovery from partial deafferentation increases 2-deoxyglucose uptake in distant spinal segments

2-Deoxy[ 14C]glucose autoradiography was used to study the responsiveness of the partially deafferented rat spinal cord to electrical stimulation of low-threshold afferent fibers. Unilateral extradural dorsal rhizotomies were carried out at L3 to S2, sparing L5. Postoperative sensory deficits were appropriate to the extent of the lesion. Acute, 7 day, and 14 to 20 day postrhizotomy animals and unoperated controls were anesthetized prior to isotope injection and electrical stimulation of Ia fibers in the L5 root. Quantitative densitometry was carried out on enlarged autoradiographs, subdividing the spinal gray matter into laminar divisions drawn from the corresponding stained sections. Optical densities from stimulated and unstimulated sides were compared using paired t tests for each experimental group at each lumbosacral segment (L1 to S2) and at T13 for the day 14 to 20 animals. This procedure provided an objective basis for statistical comparisons between homologous areas even where the differences in density were small. Unoperated animals showed activation in 11 of 23 dorsal horn zones extending to L2 and never involving the base of the dorsal horn (lamina V). Acute and day 7 groups did not appreciably differ from the control group except for activation of lamina V within the L4 segment. In the most delayed group, 18 dorsal horn regions were activated, extending to L1 with an additional zone in T13. Lamina V contained significant labeling in three segments. In no group was there increased labeling of the ventral horn. The results are interpreted as showing that stimulus-related, neural activity increases after a 2-week delay in regions of spinal cord distant from the normal zone of significant metabolic change. This increase in neural activity during recovery is discussed in relation to time-dependent electrophysiologic, structural, and metabolic responses to deafferentation. The longitudinal spread of dorsal horn activation by preserved afferent fibers in the spared root may facilitate more effective central transmission of sensory information.

Structure of the serine chemoreceptor in Escherichia coli.

Many biological processes depend on the function of proteins that detect changes in a cell's environment and transmit the information to the cytoplasm, for example, peptide hormone receptors. In Escherichia coli this class of proteins is exemplified by the sensory transducers (also called signalling proteins or methyl-accepting chemotaxis proteins) which have a central role in mediating chemotactic behaviour. The sensory transducers are the products of four genes: tsr, tar, tap and trg. Each transducer detects changes in the environmental concentration of one or a very few attractants: Tsr, serine; Tar, aspartate and maltose; Tap, unknown; and Trg, ribose and galactose. Tsr and Tar act directly as chemoreceptors for the amino acid attractants and signal changes in their degree of occupancy to the flagellar apparatus. Detection of these changes in occupancy is made possible as the transducers are methylated at multiple glutamate residues such that their level of methylation reflects the most recent chemoeffector concentration. Biochemical and genetic information concerning the serine transducer protein has been accumulating rapidly but little is known about the structure of the molecule. We present here the nucleotide sequence of the tsr gene of E. coli; the amino acid sequence derived from it suggests that the Tsr transducer protein has a relatively simple transmembrane structure that may place limits on the mechanisms available for the transmission of sensory information into the cell.

Ethanol's effect on selective gating of somatic sensory inputs to single cortical neurons

The effect of alcohol intoxication was tested on sensory responses of single units in the somatosensory (SI) cortex of awake, freely moving rats. We have previously shown that transmission of cutaneous sensory information from the paw to the cortex during movement is subject to a time varying pattern of sensory suppression which selectively “gates in” sensory information to particular categories of cortical neurons during certain phases of the locomotor step cycle. In the period of 5–20 minutes after alcohol administration (when the rats became hyperactive) the afferent inhibition producing this selective gating was reduced or abolished, depending on the ethanol dose (between 0.75 and 1.5 g/kg). This indicates that the selective suppression of “irrelevant” inputs to certain cortical cells, which is normally seen during movement, is absent during alcohol intoxication. This paradigm may provide a model for study of the neurophysiologic mechanism by which alcohol disturbs higher cognitive functions involving cortical management of sensorimotor tasks.

Evoked potentials in the dentate gyrus reflect the retention of past sensory events

Averaged sensory evoked potentials were recorded from the outer molecular layer of the dentate gyrus (OM AEP) in freely moving rats trained to criterion performance in a two-tone differential discrimination paradigm. OM AEPs showed consistent fluctuations in amplitude based on the acquired significance of the tones through their association with reward (CS+) or non-reward (CS−). However, the relationship between tone significance and OM AEP configuration was dependent upon the sequence of trials preceding the evoked potential, irrespective of whether the potential was evoked by a CS+ or CS−. Specifically, when the preceding sequence contained an increased number of CS− trials, the amplitude of the initial negative component (N 1) of the OM AEP was increased, while that of the slower (N 2) component was reduced; conversely, when the preceding sequence contained an increased number of CS+ trials, the amplitude of N 1 was reduced, while that of N 2 was increased. The results suggest that the transmission of sensory information into the dentate gyrus is biased by prior experience.

Modulation of sensory responsiveness of single somatosensory cortical cells during movement and arousal behaviors

This study tested the hypothesis that the transmission of cutaneous sensory information to single somatosensory (SI) cortical neurons may be modulated or gated during movement or “arousal” behaviors. The results showed that movement by itself was associated with a powerful suppression of the sensory input to SI cortical cells from their cutaneous receptive fields. Control experiments showed that this sensory suppression during movement could not be due to either(i) an obscuring of the sensory responses by the large increases in the spontaneous discharge rates of these cells generally found during movement, (ii) an occlusion of the sensory response to the test stimuli by the increased activity in parallel sensory channels caused by repetitive foot contact during locomotion, (iii) distraction of the animal's attention or, (iv) differences in the motivational or arousal states associated with various movement states, because sensory suppression was found in both grooming and treadmill locomotion. It was also found that, in the absence of movement, strong arousal was associated with a slight increase in sensory responsiveness and a decrease in spontaneous discharge rate. The finding that movement rather than arousal or attentiveness caused the most potent modulation of the sensory responsiveness and firing rates of SI cortical cells suggests that this cortical area may be closely integrated with central nervous system motor functions.

Interneurons coactivating hindleg flexor and extensor motoneurons in the locust

1. Using intracellular staining and recording techniques in the ventral nerve cord of locusts, we have identified a pair of large interneurons which monosynaptically excite hindleg flexor and extensor tibiae motoneurons. The somata and input processes of these interneurons are in the mesothoracic ganglion and each makes its connections to hindleg motoneurons via a large axon running in the meso-metathoracic connective contralateral to its soma. 2. We refer to these interneurons as C-neurons because single action potentials in one interneuron often caused the coactivation of the fast extensor tibiae motoneuron and a variable number of flexor tibiae motoneurons in one hindleg. The probability of activity in a C-neuron activating hindleg motoneurons depended on the position of the tibia, being highest when the tibia was flexed. 3. Coactivation of the fast extensor tibiae motoneuron and a number of flexor motoneurons could also be elicited by a variety of stimuli in intact animals when the tibiae were close to full flexion. This resulted in the tibiae being locked into full flexion and, very often, to the initiation of the co-contraction phase of the jump. We refer to this synchronous activation of hindleg flexor and extensor motoneurons in intact animals as the cocking response. 4. We propose that the C-neurons function to produce the cocking response. Consistent with this proposal is that the C-neurons receive input from all those sensory sources which evoke the cocking response. 5. A general feature of the interneuronal organization in insects derived from this and other investigations is the existence of individual interneurons for the production of single aspects of a behavior. By controlling transmission of sensory information to motoneurons via these unique interneurons, the same sensory stimulus can evoke a variety of motor response. This concept is discussed in relation to the jumping system of the locust.

Long ascending projections from substantia gelatinosa Rolandi and the subjacent dorsal horn in the rat.

Small neurons of the substantia gelatinosa Rolandi and the subjacent dorsal horn of the spinal cord have been thought to exert a direct modulatory effect only on neurons located within a distance of a few spinal segemnts. By using the technique of retorograde transport of horseradish peroxidase, however, it has been found that in the rat a significant number of these cells, particularly those of the subjacent dorsal horn, ascend many spinal segments to the lateral cervical nucleus and to the lower brainstem. These data provide an anatomic basis for a role of substantia gelatinosa Rolandi and subjacent dorsal horn cells in madulating or contributing to sensory information transmission not only in nearby segments but in far distant structures.

Effects of projected cortical epileptiform discharges on field potentials in the cat cuneate nucleus

The effects of cortical epileptiform discharges on cuneate nucleus were investigated by studying cuneate field potentials evoked by corticofugal input. Cortical events triggered a negative-positive field potential sequence on the cuneate surface analogous to that evoked by forepaw nerve stimulation. Interaction of nerve-evoked potentials in the corticofugally induced positivity resulted in an amplitude decrease of the nerve potential, especially of its positive wave. Laminar analysis of the corticofugally evoked field potential suggested that its surface positive wave consisted of two components generated at different depths in cuneate; these two components were discussed as possible field potential signs of presynaptic and postsynaptic inhibition in cuneate. The influence of corticofugal discharges on transmission of sensory information through the cuneate nucleus was determined to be inhibitory, for nerve-evoked field potentials in the cuneate output pathway (medial lemniscus) were depressed during cortical epileptiform events.

Is There a Time Quantum in Duration Experience?

Modem psychological theory states that the transmission of sensory information, as well as several aspects of motor behavior, shows periodic characteristics between 20 and 200 msec. In many cases, these time constants are derived from multimodal distributions of, for example, reaction times (Lansing, 1957), visual scanning times (Augenstine, 1955), and eye movements (Latour, 1966). The findings are interpreted as evidence for a sensory and/or motor integration period, which is considered a psychological time constant and described in terms of one of three specific theories: the discrete nonoverlapping moment (Stroud, 1955), the discrete overlapping time unit (Robinson, 1966), and the continuous running-average sampling period (Uttal, 1970). Generally speaking, psychological time is not viewed as an infinitely divisible factor, but it bears the character of a finite integration period or is built up on the basis of some final quantum. The 'quantum' theories also penetrated time perception as a more or less separate field of research. Within the framework of Treisman's model, it is assumed that the apparent duration of an interval arises from the integration of finite, nonoverlapping periods generated by an internal clock ('pulse generator'). The accelerations and decelerations of subjective time with respect to physical time are caused by speed fluctuations of the pulse generator as a function of arousal level (Treisman, 1963; see also Vroon and Van Boxtel, 1972). Creelman (1962) used the concept of a time quantum in a model describing the ability to discriminate between short intervals, and Michon (1965, 1967) directly demonstrated the existence of it in time perception.

Characteristics of projections from primary sensory cortex to motorsensory cortex in cats

The detailed organization of projections from sensorimotor cortex (Sml) to motorsensory cortex (MsI) was examined utilizing intracortical microstimulation (ICMS) in cats. The area of SmI projecting to near the lateral end of the cruciate sulcus lay near the lateral end of the postcruciate dimple. The low threshold region within the depths of SmI for exciting a given cell of MsI by ICMS was extremely restricted in the vertical direction. Comparison of peripheral receptive fields of cells in the interrelated regions of the two cortical areas shows that the two regions receive input from overlapping or contiguous peripheral loci. Blocking transmission through SmI by local cooling of SmI cortex failed to show a significant effect on the peripheral activation of cells in MsI. This suggests that this pathway is not a simple relay for transmission of sensory information to MsI.

Dependence of human sensory information transmission on distribution of stimuli.

Dependence of human sensory information transmission on distribution of stimuli.

Emerging principles of sensory coding.

EMERGING PRINCIPLES OF SENSORY CODING WILUAM R. UTTAL* Determination ofthe relationship between afferent neural message pattern and perceived experience has become one of the major problem areas in psychobiology. A wide variety ofdifferent kinds ofstudies can be classified under the general rubric of "neural coding" or, more dramatically , "breaking the neural code." In all ofthese experiments the central problem is to discover how specific characteristics ofthe sensory experience are represented by the possible parameters ofvariation ofthe nervous signals. The recent upsurge in interest and progress in this field is based upon foundations of biological simplicity and technological innovation. Sensory structures and functions are all simpler, better ordered, and more easily understood than the function and structure of the higher mental processes. Yet, like the model preparations studied in lower animals, the study ofthe sensory mechanisms can also contribute to our understanding ofneural representation in a more general way. New psychophysical techniques, new electrophysiological techniques, and new computer control and analysis techniques have all added impetus to the study ofthis set ofproblems. Certain problems ofsensory coding, under attack with the aid ofthese new methods, have proven susceptible to experimental investigation in a way which cannot be matched in the much more refractory problems of the neural basis of higher cognitive activities. The amount ofresearch data which has emerged from various laboratories in the last ten or twenty years has been massive and, compared to central neural studies, quite unequivocal. Nevertheless, there have been few attempts to consider some ofthe basic biological generalities of which each experimental result is but one exemplar. In the light of this * Laboratory ofSensory Sciences, University ofHawaii. On leave from the University ofMichigan . Address reprint requests to 1042 MHRI, University ofMichigan, Ann Arbor, Michigan 48104. 344 William R. Uttal · Sensory Ctding Perspectives in Biology and Medicine · Spring 1969 new data, it appears that some of our previously accepted notions of sensory information transmission and processing are undergoing modifications or reinterpretation. Subtle and delicate changes in our perspectives are occurring which often go almost unnoticed until they become entrenched in our scientific culture and must be transmitted to a new generation. In general, science is a conservative process, changing its formal axioms only when the data and/or clamor becomes overwhelming. The necessity for this conservatism is obvious, but there is another aspect ofthe importance ofour basic assumptions which also must be considered. Our axioms and assumptions as well as our experimental technology color the way in which we look at the data obtained from a given experiment. We tend to see what is generally consistent with our previous assumptions, and we generally tend to perpetuate established points of view. Very often a simple restatement ofan axiom can change an entire experimentaltheoretical edifice. It is for this reason that it is important that occasionally we look beyond the measuring instruments of our laboratory to the premises on which we base our observations. It is the purpose ofthis paper to overtly consider some ofthese changes by reviewing some ofthis new evidence and to call attention to the gradual metamorphosis ofour classical views, which is occurring under the pressure of this new data. This is not a completely novel effort. Many scientists have individually come to some ofthe same conclusions presented in this paper. In this current effort, though, a number ofthe currently emerging principles are collected together in a way which emphasizes the principles themselves rather than embedding them within the context of a single specific experiment. It should also be noted that many ofthe points which we make have already been made years ago by other writers. It is possible that almost any ofthese points could find an antecedent in history, so no claim to originality is intended. Wherever possible, an effort has been made to acknowledge those who have earlier made these points. The reader's attention is especially directed to the report made by MacKay [i] on a symposium on neural communication sponsored by the International Brain Research Organization. Some ofthe points made here were apparently also topics ofdiscussion at that meeting. Before we begin the main text of this discussion, it may be well to make a few specific definitions to clarify our usage of...

Cochlear implants.

I AM glad this meeting is a workshop, because most of what I have to suggest means exactly that, work. I hope I can convince you it is work worthwhile. My own personal and probably too optimistic opinion is that an artificial inner ear will eventually be able to provide at least marginal hearing for some persons with sensorineural deafness. However, it should be perfectly clear that such a device is at least several years in the future, and not applicable to every deaf person. I am not referring to the crude kinds of artificial stimulation of the auditory nerve that have been known for a hundred years. Such methods might prove adequate for some sophisticated form of Morse code, but that is about all. If we are to achieve even marginally adequate transmission of sensory information by artificial methods we need to provide a great variety of auditory sensations

Transmission of sensory information through the lemniscal pathway during sleep.

Transmission of sensory information through the lemniscal pathway during sleep.

The transfer function of a photoreceptor organ.

The dynamic response of a simple ganglionic photoreceptor has been studied. It exemplifies the general processes of sensory reception and transmission of sensory information in the form of trains of nerve impulses. The experimental basis of the defining linear transfer function is presented. This transfer function is composed of a second order lag and a transport delay. The ventral nerve cord conduction time does not contribute to the transport delay. Nonlinear discrepancies from the linear model are evaluated and discussed.

A note on temporal coding as a mechanism in sensory perception

Neurone theory and the concept of the all-or-none nerve impulseare fundamental to modern neurophysiology; but the simplest ideas derived from these lead to the difficulty as to how complex sensory perception is possible through such limited structure. Recent studies suggest the possibility that in the visual system of man over-all temporal patterns of activity may be used for the transmission of certain sensory information. It is possible that this temporal coding may arise from the differing nerve impulse conduction velocities that exist in a nerve fiber bundle. Such a coding system may have a significant part to play in the general functioning of the nervous system.