Polydipsia in the monkey generated by visual display schedules.

Discussions of adjunctive behavior still largely refer to polydipsia induced by food delivery schedules to food deprived animals. In the present experiment polydipsia was induced when socially isolated monkeys housed in barren home cages were exposed to scheduled deliveries of film and scheduled viewing of other monkeys. These data suggest the greater generality and complexity of adjunctive behaviors and show that schedule-induced polydipsia cannot be regarded as an artifact of food associated drinking.     

Functional interactions among neurons in inferior temporal cortex of the awake macaque

Summary Functional interactions among inferior temporal cortex (IT) neurons were studied in the awake, fixating macaque monkey during the presentation of visual stimuli. Extracellular recordings were obtained simultaneously from several microelectrodes, and in many cases, spike trains from more than one neuron were extracted from each electrode by the use of spike shape sorting technology. Functional interactions between pairs of neurons were measured using cross-correlation. Discharge patterns of single neurons were evaluated using auto-correlation and PST histograms. Neurons recorded on the same electrode (within about 100 n) had more similar stimulus selectivity and were more likely to show functional interactions than those recorded on different electrodes spaced about 250 to 500 microns apart. Most neurons tended to fire in bursts tens to hundreds of milliseconds in duration, and asynchronously from the stimulus induced rate changes. Correlated neuronal firing indicative of shared inputs and direct interactions was observed. Occurrence of shared input was significantly lower for neuron pairs recorded on different electrodes than for neurons recorded on the same electrode. Direct connections occurred about as often for neurons on different electrodes as for neurons on the same electrode. These results suggest that input projections are usually restricted to less than 500 m patches and are then distributed over greater distances by intrinsic connections. Measurements of synaptic contribution suggest that typically more than 5 near-simultaneous inputs are required to cause an IT neuron to discharge.     

Changes in the P100 latency of the visual evoked potential and the saccadic reaction time during isometric contraction of the shoulder girdle elevators

We investigated changes in the P100 latency of the visual evoked potential (VEP) and the saccadic reaction time (SRT) in relation to the degree of activity of the shoulder girdle elevators. Muscle force was set in 10% increments from 0% to 50% of the maximal voluntary contraction (MVC). The VEP was derived from a midline occipital electrode with reference electrodes on the ears when the right retina was stimulated through the eyelid by light emitting diodes while the eyes were closed. The P100 latency of the VEP was defined as the time from the stimulus onset to the main positive peak. The SRT was defined as the latency until the beginning of eye movement toward the lateral target, which was moved at random time-intervals. P100 latency was shortened until 30% of the MVC, and which it lengthened. The SRT changed in a pattern similar to that observed for the P100 latency. The ratio of the shortening in P100 latency relative to that of the SRT was approximately 20%. All data is presented as the mean value, plus the standard deviation. We believe that the information processing time in the neural pathway from the retina to the visual cortex was shortened up to a certain muscle force of the shoulder girdle elevators, and then this processing time lengthened. These findings indicate that shortening of information processing time in the neural pathway beyond the visual cortex is included in the shortening of the SRT.     

Differential responsiveness of simple and complex cells in cat striate cortex to visual texture

Summary The responsiveness of 254 simple and complex striate cortical cells to various forms of static and dynamic textured visual stimuli was studied in cats, lightly anaesthetised with N₂O/O₂ mixtures supplemented with pentobarbitone.Simple cells were unresponsive to all forms of visual noise presented alone, although about 70% showed a change in responsiveness to conventional bar stimuli when these were presented on moving, rather than stationary, static-noise backgrounds. Bar responses were depressed by background texture motion in a majority of cells (54%), but were actually enhanced in a few instances (16%).In contrast, all complex cells were to some extent responsive to bars of static visual noise moving over stationary backgrounds of similar texture, or to motion of a whole field of static noise. The optimal velocity for noise was generally lower than for bar stimuli.Since moving noise backgrounds were excitatory for complex cells, they tended to reduce specific responses to bar stimulation; in addition, directional bias could be modified by direction and velocity of background motion.Complex cells fell into two overlapping groups as regards their relative sensitivity to light or dark bars and visual noise. Extreme examples were insensitive to conventional bar or edge stimuli while responding briskly to moving noise.In many complex cells, the preferred directions for motion of noise and of an optimally oriented black/white bar were dissimilar.The ocular dominance and the degree of binocular facilitation of some complex cells differed for bar stimuli and visual texture.Preliminary evidence suggests that the deep-layer complex cells (those tolerant of misalignment of line elements; Hammond and MacKay, 1976) were most sensitive to visual noise. Superficial-layer complex cells (those preferring alignment) were less responsive to noise.Only complex-type hypercomplex cells showed any response to visual noise.We conclude that, since simple cells are unresponsive to noise, they cannot provide the sole input to complex cells. The differences in the response of some complex cells to rectilinear and textured stimuli throw a new light on their rôle in cortical information-processing. In particular, it tells against the hypothesis that they act as a second stage in the abstraction of edge-orientation.     

Peak Identification in Visual Evoked Potentials

Waveform patterns evoked by 4 intensities of flash in normal subjects were studied in relation to intersubject variability. Time-frequency distribution curves of all peaks occurring between 11 and 280 msec after flash onset and meeting minimal criteria were obtained from 46 males. These distributions closely corresponded to similar data reported by others for single intensity stimulation. An algorithm was developed which identified in 67 to 100% of instances a single “peak event’ within the time ranges of each of 6 peak distributions. Many peak events appeared and disappeared within the 4 intensity sets of individuals. Latencies were obtained for these peak events. Application of the algorithm to a replicate sample of 29 Ss, which included 8 females, indicated generalizability. Test-retest data on 15 Ss showed its reliability. The data suggest that methodology significantly contributes to the variability of peak identification among subjects. This may be reduced by employing multiple intensities of stimulation.     

Visual perception in women during the menstrual cycle

Twelve females were tested at four times during the menstrual cycle with a visual detection task and a visual pattern discrimination task. Mood levels and confidence ratings were evaluated for each session. In addition to the behavioral testing, plasma samples were collected and radioimmunoassayed for estradiol, progesterone, luteinizing hormone, and follicle stimulating hormone levels. Visual detection fluctuated significantly during the menstrual cycle with impaired performance occurring at the premenstrual session. In contrast to previous reports, the impaired performance was not related to lowered confidence ratings or to mood levels.     

Hemi-field pattern visual evoked potentials: A comparison of display and analysis techniques

Summary Three methods for analyzing the spatial organization of visual evoked potentials were compared. Pattern reversal visual evoked potentials were obtained from a single subject under three viewing conditions: stimulation of the left, right, and both visual fields. The scalp distribution of the VEP to 1 deg checks was displayed using three recording and analysis techniques: a conventional horizontal occipital array of electrodes, topographic mapping, and 3-dimensional evoked potentials. All three techniques revealed "paradoxical" lateralization of P100. The relative merits of each technique are discussed.We are grateful to Susan Hoffmann-Nader and Rebecca Clark-Bash for data collection. This research was supported in part by the Brain Research Foundation of the University of Chicago.     

Frequency and luminance sensitivity of visual evoked response in developing rats

Recent advances in the study of evoked responses settled a definition of transient and steady-state visual evoked responses (VER) and discovered the existence of Temporal Frequency Regions in humans. This paper reports data from visual responses evoked by low and high frequency stimuli. White flashes were performed in albino Sprague Dawley rats from 7 to 90 days of age. Frequency analysis technique offered the possibility to evaluate the amplitude parameters and their variations dependent on intensity of luminance and on development. The responses suggested the existence of two temporal frequency regions in the rat: a first one at about 8 Hz, related to high frequencies of EEG, a second one at frequencies ranging from 12 to 24 Hz, related to luminance sensitivity. The development of the second region is correspondent to the complete development of transient VER parameters.     

Simple mechanical-chemical systemic pressure-control device

An implantable mechanical-chemical device was constructed to act as a feedback mechanism in controlling the blood pressure. It consisted of a balloon connected to a rubber catheter ending in a slit valve. Flow-pressure curves were derived fromin vitro testings for three valve thresholds (120, 140 and 170 mmHg). Five fast-acting hypotensive drugs subsequently filled the device during 40 noradrenaline infusions in 25 dogs, with the balloon in the abdominal aorta and the catheter in the inferior vena cava. The results were as follows: (i) Following a short initial increase in systolic aortic pressure, significantly lower (p<0·001) than in control experiments, the device prevented any pressure rise above its threshold. (ii) The time needed for pressure lowering at the device's threshold depended on the drug used being 3·34±0·84 (mean ± s.e. in minutes) for sodium nitroprusside, 5·99±0·96 for phentolamin, 11·63±2·97 for hydralazine, 14·54±2·43 for a-methyl-dopa and 23·32±2·07 for diazoxide.     

Sensory-feedback system compatible with myoelectric control

Progress in the development of a system to provide sensory feedback of the pinch force of an artificial hand is described. Design criteria relating to electrocutaneous stimulation and compatibility with myoelectric control are discussed. Details of a practical system, presently in use by two amputees prior to full-scale clinical evaluation, are presented.