The RF-cinematogram. A cross-correlation technique for mapping several visual receptive fields at once

We present a spike-triggered averaging method capable of mapping the visual receptive fields of several neurons simultaneously. The stimulation is general and the mapping proceeds automatically without the need to match the stimulation to the cells' preference for position, orientation, direction, etc. The maps are spatiotemporal; receptive field (RF) structures are quantitatively determined in three dimensions: the two dimensions of visuotopic space, and time. The method presented is one of a family of "reverse correlation" or "spike-triggered averaging" techniques (DeBoer and Kuyper 1968) capable of revealing linear aspects of stimulus-response coupling. The formal relationship of these methods to stimulus-response cross-correlation is shown. The analysis is extended to provide some second-order axis-of-motion information ("direction marks"). The stimulus is a constantly illuminated, randomly jumping bright or dark spot, not an elongated bar. Spot diameters between one-third to 1 x RF width are effective. The method ascertains for each recorded action potential or "spike" the prior visual field position of the spot. The average or most probable spot positions define the receptive field spatially. Repeating the process for a succession of times prior to observed spikes defines the field temporally, presented here as a succession of spatial maps. We term this portrayal a receptive field cinematogram, RFc or ciné. The RFc reveals and economically portrays the spread of excitability and suppression across the receptive field, culminating in the generation of a spike. RFcs for LGN neurons and for simple cells recorded in cat cortical areas 17 and 18 are presented and interpreted in terms of classic ON/OFF regions. The availability of temporal information permits the separation of an excitatory exit response, generated when a moving bright spot leaves an OFF region, from an excitatory entrance response occurring when a bright spot enters an ON region, because these responses occur at different times (exit responses earlier). Spike emission remains coupled to (cross-correlated with) stimulus events over time periods as long as 96 ms, implying that some stimulus drive or afferent visual input is delayed by as much as 96 ms more than other input. This is a striking instance of temporal dispersion in the visual system. In some cells, said to be "spatiotemporally inseparable", the delay (latency) varies systematically across the visual field; i.e., the place for optimal stimulation varies with the time prior to spike emission. In these cells, the RFc shows receptive field structures which move across the visual field over trajectories equal to approximately twice the total conventional RF width.(ABSTRACT TRUNCATED AT 400 WORDS)

[Knowledge of carcinogenic and immunologic findings caused by the zeolite fiber erionite]

Prompted by the unusually high death rate from cancer of the lungs, in 1975 in the Middle-Anatolian village of Karain, later in two other villages, X-ray screening investigations were carried out. These revealed pleural mesotheliomas similar to those seen following exposure to asbestos, although no asbestos was found neither in the village itself or in its immediate surroundings. Minerological tests and examinations of the lungs of the deceased, together with animal experiments involving dust obtained from the village itself, performed in 1980, demonstrated that erionite, a fibrous zeolite is responsible for tumour lesions in the lungs and pleura. Early stages of this tumour located in the pleura were also found in a group of Karain inhabitants working in Sweden. On the basis of the examination results, an immune deficiency that did not correlate with age, sex or duration of exposure was found, and thus cannot readily be classified as an epiphenomenon. Since fibrous zeolites are frequently employed in industry, industrial hygiene and occupational medical consequences need to be drawn.

[BCG vaccination and the incidence of tuberculosis in students of urban Kayseri, Turkey]

The rate of new infections with tuberculosis amounting to approximately 20% among the youngest inhabitants of the town of Kayseri with a present recorded incidence of acute infectious tuberculosis of about 8:10000 makes it imperative to exercise every possible effort in disease prevention by vaccination and revaccination in addition to all other measures to combat tuberculosis.

Stereoscopic mechanisms in monkey visual cortex: binocular correlation and disparity selectivity

The neural signals in visual cortex associated with positional disparity and contrast texture correlation of binocular images are the subject of this study. We have analyzed the effects of stereoscopically presented luminous bars and of dynamic random-dot patterns on the activity of single neurons in cortical visual areas V1, V2, and V3-V3A of the alert, visually trained rhesus macaque. The interpretation of the results and considerations of possible neural mechanisms led us to recognize 2 functional sets of stereoscopic neurons. (1) A set of neurons, tuned excitatory (T0) or tuned inhibitory (TI), which respond sharply to images of zero or near-zero disparity. Objects at or about the horopter drive the T0 neurons and suppress the TI, while objects nearer and farther have the opposite effects on each type, inhibition of the T0 and excitation of the TI. The activity of these neurons may provide, in a reciprocal way, the definition of the plane of fixation, and the basic reference for binocular single vision and depth discrimination. (2) A second set of neurons includes tuned excitatory at larger crossed or uncrossed disparities (TN/TF) and neurons with reciprocal excitatory and inhibitory disparity sensitivity with cross-over at the horopter (NE/FA). Binocularly uncorrelated image contrast drives these neurons to a maintained level of activity, which shifts, in response to correlated images, toward facilitation or suppression as a function of positional disparity. These neurons may operate in the neural processing leading to stereopsis, both coarse and fine, and also provide signals for the system controlling binocular vergence. These results indicate that cortical visual neurons are binocularly linked to respond to the relative position and contrast of the images over their receptive fields, and also that both these aspects of binocular stimulation may be utilized by the brain as a source of stereoscopic information.

Alpha-1 and alpha-2 adrenoceptor agonists induce vasoconstriction of the normotensive rat caudal artery in vitro by stimulation of a heterogeneous population of alpha-1 adrenoceptors

Although alpha-2 adrenoceptor agonists rapidly induce arterial vasoconstriction in vivo, such responses have proven difficult to obtain in vitro. We have investigated the vasoconstrictor effects of various alpha-1 and alpha-2 adrenoceptor agonists in the perfused superfused caudal artery of the normotensive rat. Intrinsic activities were; methoxamine; 1, phenylephrine; 0.94, noradrenaline; 0.93, guanfacine; 0.88, clonidine; 0.47, UK 14,304 [5-bromo-6-(2-imidazoline-2-ylamino)-quinoxaline tartrate]: 0.10, azepexole; 0. Antagonism by the selective alpha-1 agent, prazosin of the vasoconstrictor responses provoked by methoxamine, guanfacine or clonidine, showed a high affinity with--log KB values in the range of 8.5 to 9.4. There were no significant differences between the KB values obtained with the three agonists. Antagonism by the selective alpha-2 antagonist, yohimbine showed a low affinity with KB values between 6.7 to 7.6 for the three agonists. The calcium entry blocker, nicardipine, antagonized responses to clonidine at nanomolar concentrations and those to phenylephrine at micromolar concentrations. We conclude that vasoconstrictor responses in this isolated tail artery preparation are primarily mediated via an alpha adrenoceptor which can be classified, on the basis of the results with specific antagonists, as being of the alpha-1 type. The results obtained with nicardipine suggest that the population of alpha adrenoceptors is not, however, homogeneous.

[Agastric dystrophy after gastrectomy]

A follow-up of 9 patients was performed 5-11 years subsequent to total gastrectomy. Biochemical findings were normal. Compared to a normal control group vitamin A absorption indicative of fat assimilation was unaltered. Subjects regained preoperative weight and presented no signs of malnutrition. Eight patients suffered seriously from reflux. Five patients showed dumping symptoms. Endoscopic specimens from jejunal mucosa were found to be normal. It seems that postoperative complaints described above may be prevented by reasonable operative measures.