Dynamics of history-dependent perceptual judgment

ABSTRACTIdentical physical inputs do not always evoke identical percepts. To investigate the role of stimulus history in tactile perception, we designed a task in which rats had to judge each vibrissal vibration, in a long series, as strong or weak depending on its mean speed. After a low-speed stimulus (trial n-1), rats were more likely to report the next stimulus (trial n) as strong, and after a high-speed stimulus, they were more likely to report the next stimulus as weak, a repulsive effect that did not depend on choice or reward on trial n-1. This effect could be tracked over several preceding trials (i.e. n-2 and earlier) and was characterized by an exponential decay function, reflecting a trial-by-trial incorporation of sensory history. Surprisingly, the influence of trial n-1 strengthened as the time interval between n-1 and n grew. Human subjects receiving fingertip vibrations showed these same key findings. We are able to account for the repulsive stimulus history effect, and its detailed time scale, through a single-parameter model, wherein each new stimulus gradually updates the subject’s decision criterion. This model points to mechanisms underlying how the past affects the ongoing subjective experience.

The Habituation/Cross-Habituation Test Revisited: Guidance from Sniffing and Video Tracking

The habituation/cross-habituation test (HaXha) is a spontaneous odor discrimination task that has been used for many decades to evaluate olfactory function in animals. Animals are presented repeatedly with the same odorant after which a new odorant is introduced. The time the animal explores the odor object is measured. An animal is considered to cross-habituate during the novel stimulus trial when the exploration time is higher than the prior trial and indicates the degree of olfactory patency. On the other hand, habituation across the repeated trials involves decreased exploration time and is related to memory patency, especially at long intervals. Classically exploration is timed using a stopwatch when the animal is within 2 cm of the object and aimed toward it. These criteria are intuitive, but it is unclear how they relate to olfactory exploration, that is, sniffing. We used video tracking combined with plethysmography to improve accuracy, avoid observer bias, and propose more robust criteria for exploratory scoring when sniff measures are not available. We also demonstrate that sniff rate combined with proximity is the most direct measure of odorant exploration and provide a robust and sensitive criterion.

Raphe obscurus neurons participate in thermoregulation in rats

In mammalian, several evidences suggest that central serotonin participates in thermoregulation. Nucleus raphe obscurus (NRO), a serotonergic nucleus, has been recognized to be the source of generation of various hemodynamic patterns in different behavioral conditions, but its involvement in thermoregulation is unclear. In the present study, extracellular action potentials of NRO neurons were recorded in anesthetized rats, which were submitted to cold and warm stimuli in the tail. The firing rate of the neurons was compared before and after each stimulation. It was found that 59% of the neurons submitted to a cold stimulus trial had a significant increase in their firing frequency, while 48% of the neurons submitted to warm stimulation trial were inhibited. The opposite responses in neuronal activity of NRO units to cooling or heating suggest that these cells are involved in producing the homoeothermic vascular adaptations secondary to changes in cutaneous temperature in the rat tail.

Influence of central antitussive drugs on the cough motor pattern

The present study was conducted to determine the effects of administration of centrally active antitussive drugs on the cough motor pattern. Electromyograms of diaphragm and rectus abdominis muscles were recorded in anesthetized, spontaneously breathing cats. Cough was produced by mechanical stimulation of the intrathoracic trachea. Centrally acting drugs administered included codeine, morphine, dextromethorphan, baclofen, CP-99,994, and SR-48,968. Intravertebral artery administration of all drugs reduced cough number (number of coughs per stimulus trial) and rectus abdominis burst amplitude in a dose-dependent manner. Codeine, dextromethorphan, CP-99,994, SR-48,968, and baclofen had no effect on cough cycle timing (CTtot) or diaphragm amplitude during cough, even at doses that inhibited cough number by 80–90%. Morphine lengthened CTtot and inhibited diaphragm amplitude during cough, but these effects were not dose dependent. Only CP-99,994 altered the eupneic respiratory pattern. Central antitussive drugs primarily suppress cough by inhibition of expiratory motor drive and cough number. CTtot and inspiratory motor drive are relatively insensitive to the effects of these drugs. CTtot can be controlled independently from cough number.

SELECTION PREFERENCE OF STARTER PIGS FED CANOLA MEAL AND SOYBEAN MEAL SUPPLEMENTED DIETS

Selection preferences of starter pigs (4–5 wk old) fed diets supplemented with soybean meal (SBM) and canola meal (CM) with or without added flavor were studied in four experiments. In exp. 1, starter pigs were offered a choice between a SBM control diet and one of four isonitrogenous, isoenergetic CM supplemented diets containing either 5, 10, 15 or 20% CM. From 5 to 9 wk of age, pigs consumed two and one-half to seven times more SBM control diet than diets containing 5–20% CM, respectively. In exp. 2, the influence of supplementary monosodium glutamate (0.15%), dextrose (10%) and corn oil (4 and 5%) on the consumption of diets in which CM replaced 50–100% of the protein supplied by SBM was studied. No significant differences in feed intake or pig performance were attributed to the addition of these additives to the CM diets. In experiments three and four, the effect of flavor additives (Pig Krave and Hy Sugr ADE) on the palatability of CM supplemented diets was determined. In exp. 3, feed intake of pigs fed diets containing 100% CM with added flavors was significantly greater than that of pigs fed the 100% CM nonflavored diets. In exp. 4, a single stimulus trial, pigs consumed more (P < 0.001) of the flavored CM diets than the nonflavored diets. The improved feed intake of flavored CM supplemented diets decreased as the level of dietary CM increased. Key words: Palatability, flavor additives, starter pigs, canola meal, soybean meal

A dorsal spinal neural network in cat. I. Responses to single impulses in single type I cutaneous input fibers

1. We have studied some properties of a sacral dorsal spinal gray matter network. the lamina 4:type 1 afferent fiber network (L4:T1 network) in 24 adult cats that were anesthetized with urethan and the spinal cord transected at the thoracolumbar junction. 2. The network in the first sacral segment is composed of a subgroup of lamina 4 cells as principal neurons that are connected to type 1 afferent fibers emerging from the skin, the manipulable input channels. Other primary afferent fibers and axons of central cells of other segments may also be input elements. Cells of the substantia gelatinosa (SG) and of the marginal layer constitute the intrinsic neurons. We monitored the output of the network by unit recording of the lamina 4 cell's impulse activity. 3. We activated the network by single impulses delivered via single type 1 afferent fibers. We stimulated fibers individually by focused electrical stimulation and monitored the selectivity of the stimulus by a computer-averaging procedure. The basic stimulus paradigm (each stimulus trial) consisted of 100 single impulses delivered 1 impulse/3 s. For nine networks, each of the accessible type 1 fibers was used as an input channel. 4. The typical pattern of response to the 100 impulses was composed of: a) an early discharge lasting for 5 ms after the input impulse invades the central arbor of the type 1 fiber, b) a late discharge of variable duration terminated by c) a postresponse reduction in ongoing discharge rate. Early-only and late-only discharges were occasionally observed. We conclude that the response pattern reflects the specific neuronal and synaptic configuration that is engaged by each input channel. 5. Across input channels, the early discharge was characterized by: a) a bimodal distribution of low- and high-probability responses, reflecting two predominating groups of type 1 input channels, one believed to be weakly coupled and the other strongly coupled to the principal neuron; b) relatively little multiple discharge; c) modal response during the first 2 ms of the discharge; d) response produced via a monosynaptic connection of the type 1 fiber with the lamina 4 neuron and average synaptic delay of 0.53 +/- 0.01 ms (mean +/- SE, n = 100); e) in general, a stable response throughout the 5-min stimulus trial, although an occasional habituating response was noted. 6. The late discharge was characterized by: a) a multiple discharge and a wide response jitter; b) mean duration approximately 29 ms; c) in general, high-probability response; d) a tendency for the response to wane during the course of the stimulus trial. 7. We observed no relationship between the magnitude of the early or late response and the level of ongoing discharge when considered across input channels. However, for a given input channel over time, the output response was often highly correlated with the level of ongoing discharge. The effect was best described by a log-log relationship...