Possible interactions between visual and tactile memories in octopus

Octopuses were trained first with a tactile and then a visual discrimination and the two sets of memories were then made to conflict. A negative visual memory (white) blocks the effect of a previously learned positive tactile memory (either rough or smooth) but only in the period immediately after seeing the colour. There is no longer‐term effect on the positive tactile memory. A positive visual memory (black) was not able to reverse a previously learned negative tactile memory (rough). A negative tactile memory (rough) had no effect on previously established positive visual memories (black or white).

The only interactions between the visual and tactile memories are a result of the sharing of final common paths to the arms. There is no good evidence of second order conditioning under these circumstances.     

Monosodium glutamate and sweet taste: discrimination between the tastes of sweet stimuli and glutamate in rats

Generalization of a conditioned taste aversion (CTA) is based on similarities in taste qualities shared by the aversive substance and another taste substance. CTA experiments with rats have found that an aversion to a variety of sweet stimuli will cross-generalize with monosodium glutamate (MSG) when amiloride, a sodium channel blocker, is added to all solutions to reduce the taste of sodium. These findings suggest that the glutamate anion elicits a sweet taste sensation in rats. CTA experiments, however, generally do not indicate whether two substances have different taste qualities. In this study, discrimination methods in which rats focused on perceptual differences were used to determine if they could distinguish between the tastes of MSG and four sweet substances. As expected, rats readily discriminated between two natural sugars (sucrose, glucose) and two artificial sweeteners (saccharin, SC45647). Rats also easily discriminated between MSG and glucose, saccharin and, to a lesser extent, SC45647 when the taste of the sodium ion of MSG was reduced by the addition of amiloride to all solutions, or the addition of amiloride to all solutions and NaCl to each sweet stimulus to match the concentration of Na+ in the MSG solutions. In contrast, reducing the cue function of the Na+ ion significantly decreased their ability to discriminate between sucrose and MSG. These results suggest that the sweet qualities of glutamate taste is not as dominate a component of glutamate taste as CTA experiments suggest and these qualities are most closely related to the taste qualities of sucrose. The findings of this study, in conjunction with other research, suggest that sweet and umami afferent signaling may converge through a taste receptor with a high affinity for glutamate and sucrose or a downstream transduction mechanism. These data also suggest that rats do not necessarily perceive the tastes of these sweet stimuli as similar and that these sweet stimuli are detected by multiple sweet receptors.     

The relationship between the side tastes of masking stimuli and masking in binary mixtures

Subjects estimated the sweetness of HOH, NaCl, Q₂SO₄, sucroseand of the binary mixture of the three compounds. Another groupof subjects made independent estimates of the bitterness andsaltiness of HOH, Q₂SO₄, NaCl and of the binary mixtures ofNaCl and Q₂SO₄. Apart from their specific main taste, the stimuliappear to also possess a side taste in the modality equal tothe suppressed component, with the exception of Q₂SO₄ whichshowed no sweet side taste. The side tastes are negatively relatedto masking, thus the higher a specific side taste, the lowerthe amount of suppression of that taste in the binary mixture.Apparently, the subjects add these side tastes of the maskingagents to the specific quality of the suppressed sensationsin the mixture. In this way spurious results of low maskingor even enhancement are produced. The obtained results werecompared to data from a study in the literature on taste masking.     

Social facilitation of insect reproduction with motor-driven tactile stimuli

Tactile stimuli provide animals with important information about the environment, including physical features such as obstacles, and biologically relevant cues related to food, mates, hosts and predators. The antennae, the principal sensory organs of insects, house an array of sensory receptors for olfaction, gustation, audition, nociception, balance, stability, graviception, static electric fields, and thermo-, hygro- and mechanoreception. The antennae, being the anteriormost sensory appendages, play a prominent role in social interactions with conspecifics that involve primarily chemosensory and tactile stimuli. In the German cockroach (Blattella germanica) antennal contact during social interactions modulates brain-regulated juvenile hormone production, ultimately accelerating the reproductive rate in females. The primary sensory modality mediating this social facilitation of reproduction is antennal mechanoreception. We investigated the key elements, or stimulus features, of antennal contact that socially facilitate reproduction in B. germanica females. Using motor-driven antenna mimics, we assessed the physiological responses of females to artificial tactile stimulation. Our results indicate that tactile stimulation with artificial materials, some deviating significantly from the native antennal morphology, can facilitate female reproduction. However, none of the artificial stimuli matched the effects of social interactions with a conspecific female.     

Incidental learning and memory for three basic tastes in food

Forty three subjects were invited under the pretence that they would take part in an experiment on hunger feelings. They came without having eaten anything that morning and received a standard breakfast containing orange juice, cream cheese on crackers and yoghurt. These products were later (when subjects returned after scoring hunger feelings during the day) used as targets amidst a set of distractors varied by adding or subtracting different amounts of two basic tastes. Orange juice was varied in sweetness and bitterness, cream cheese in sourness and bitterness and yoghurt in sweetness and sourness. The changes were made comparable by using just noticeable differences, determined in preliminary experiments with other subjects, as units of change. Two measurements of memory were compared, an absolute (indicating which were the targets) and a relative one (indicating whether the targets and distractors were more, less or equally pleasant, sweet, sour, bitter or salty as the item eaten at breakfast). Both methods showed incidental learning, but relative memory was superior. Memory differed between tastes and was partly product dependent. These experiments suggest that taste memory is tuned to detect novel and potentially dangerous stimuli rather than to remember features of earlier experienced stimuli with great precision.     

Model investigation of neuronal mechanisms of discrimination between two tactile stimuli in snails

Synaptic and spike responses of neurons were studied in a two-layered model based on a study of the structure of the neuronal net of the defensive reflex in snails [4], using a technique of simultaneous application of two equal stimuli. When the points of application of the two stimuli were brought closer together the bimodal distribution of synaptic and spike responses of the efferent neurons of the model gradually changed into unimodal. The character of quantitative changes in synaptic and spike responses of neurons of the model, as the points of application of the two stimuli move closer together, reflects well the character of changes in effector responses of the snail's foot under experimental conditions as the distance between the two simultaneously acting tactile stimuli is reduced. After removal of the CNS, responses of contraction of the foot muscles of the snail become less accurate (they have a more diffuse maximum). It is suggested that the difference between functions of the central and peripheral nerve nets in molluscs lies in differences in the degree of accuracy of performance of the reflex response.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 15, No. 6, pp. 604–610, November–December, 1983.     

Direct and feedback temporary connections between unfamiliar visual stimuli]

Recording of averaged evoked potentials to two successive visual stimuli shows that associations, temporary connections, direct and feedback, can be elaborated in man between two unrecognized stimuli. The magnitude of cortical late response to the first stimulus in the complex diminishes as a result of action of the inhibitory feedback temporary connection. This inhibitory effect is more pronounced when the second stimulus is emotionally significant for the subject. The evoked potential to the second stimulus in the association between unrecognized visual stimuli is considerably facilitated. The role is discussed of direct and feedback temporary connections between unrecognized stimuli in some unconscious psychic phenomena in man.     

Goldfish's visual information processing patterns in food-reinforced discrimination learning between compound visual stimuli

Summary To examine how goldfish process and store information on compound visual stimuli, goldfish were trained with visual discriminative stimuli composed of varied colors and patterns using a Y-maze instrumental conditioning technique. The fish showed some very different types of information processing patterns depending upon the degree of discrimination difficulty of each constituent aspect (color and pattern). Those trained with compound stimuli with both a more easily discriminated aspect and a more difficult aspect learned the former selectively but did not learn the latter at all in spite of a high rate of training. Contrary to this, the fish trained with compound stimuli composed of two aspects with similar degrees of discrimination difficulty learned both aspects. In this case, only when fish were trained with compound stimuli composed of relatively more difficult aspects did they learn to discriminate between the stimuli more rapidly than the fish in each group trained with the constituent colored or patterned stimuli. These results were discussed in relation to visual processing patterns reported in other species and the mechanism of aspect selection.Abbreviations CP compound stimuli composed of VR and HB (7-mm ISBBs) - Cp compound stimuli composed of VR and HB (14-mm ISBBs) - cP compound stimuli composed of VG and HB (7-mm ISBBs) - cp compound stimuli composed of VG and HB (14-mm ISBBs) - HB horizontal patterns on blue background - HGra horizontal patterns on gray background - ISBBs interval spaces between bars - VG vertical patterns on green background - VGra vertical patterns on gray background - VR vertical patterns on red background     

Thermal versus tactile stimuli and audible vocalization in rat pups

The influences of thermal and tactile stimuli on the audible vocalization in pup rats,Rattus norvegicus were investigated. Mother rats and their litters were exposed to ambient temperature (AT) depression by 5°C for 2 hours every other day from 3 to 11 days postpartum. Nearly all audible calls emitted by pups were recorded during tactile contact with the mother. AT depression alone neither prolonged the total duration of pup-licking by mother nor intensified audible vocalization. It was found, however, that the frequency (No./h.) of nest exiting by the dam doubled during the cooling and that the sum of audible peeps emitted by cooled pups in 4 cooling days was higher than sum of peeps emitted by the control pups. This difference is apparently related to an increase in the mother's motor activity, especially nest-building activity, during cooling. Analysis of circumstances accompanying peep emission supports the hypothesis that the tactile stimuli delivered by mother play the predominant role in causing audible vocalization in pup rats. This investigation was supported by Project CPBP-04.01. of the Polish Academy of Science     

Relationship between testosterone and interest in sexual stimuli: the effect of experience

Testosterone is commonly thought to drive male sexual interest, but little experimental evidence demonstrates a direct relationship between natural variation in testosterone and sexual interest in healthy young men. This study measured young men's testosterone levels and their interest in visual sexual stimuli across three test sessions within 1 month. Fifteen men aged 23–28 viewed pictures of couples engaged in sexually explicit activity. Each session included a unique set of 72 pictures depicting heterosexual oral sex or intercourse presented in randomized order. Participants controlled how long they viewed each picture, with viewing time indicating sexual interest. Men's testosterone (T) levels were assayed from blood spots obtained prior to viewing the pictures. Overall, T and viewing time were positively correlated; however, the strength of this relationship varied by test session. T was marginally correlated with viewing time during the first session (r = 0.43) and not significantly correlated with viewing time on the second session (r = 0.16). During the final test session, when habituation might influence male interest in the stimuli, T was strongly correlated with viewing time (r = 0.80). Thus, the current study demonstrates a direct but context dependent relationship between testosterone and sexual interest in healthy young males.     

Cognitive neuroscience: feedback for natural visual stimuli

Recurrent signals in the brain are often associated with slower sensory and cognitive processes. Such patterns of activity may also form the basis of rapid perception.     

Relationship between numbers and frequencies of stimuli in human muscle fatigue

The effect of stimulus frequency on the rate of muscle fatigue has been studied on dorsiflexor muscles of the human ankle. It was found that significantly fewer stimuli were required to abolish twitch and tetanic torque when the stimuli were delivered at 15 Hz rather than 30 Hz. At both stimulus frequencies twitch torque disappeared before tetanic torque. The difference in numbers of stimuli required for fatigue was not due to impaired excitation of muscle fibers at either of the two frequencies. At both stimulating frequencies, twitch fatigue appeared to be due to a defect in excitation-contraction coupling and/or the contractile machinery.     

Selection of visual hierarchical stimuli between global and local aspects in men and women

Sex differences in global-local hemispheric selective processing were examined by hierarchical letter presenting in conditions of their perception and comparison. Fifty-six right-handed males and 68 females (aged 17-22 years) participated in the experiment. During interference between global and local aspects of stimuli the mean reaction times for correct global responses was quicker than local responses, and the right hemisphere has been dominated during global selective processing independently from the sex. Sex differences in perception of visual hierarchical stimuli were more pronounced than in comparison condition: men prefer mostly the right-hemispheric global strategy of information processing, but women--the left-hemispheric local one. Dominance of global strategy in men and local strategy in women during visual hierarchical stimuli perception together with no sex differences in correct responses indicates possibility of similar results in cognitive activity by different ways.     

Effects of fusion between tactile and proprioceptive inputs on tactile perception

Tactile perception is typically considered the result of cortical interpretation of afferent signals from a network of mechanical sensors underneath the skin. Yet, tactile illusion studies suggest that tactile perception can be elicited without afferent signals from mechanoceptors. Therefore, the extent that tactile perception arises from isomorphic mapping of tactile afferents onto the somatosensory cortex remains controversial. We tested whether isomorphic mapping of tactile afferent fibers onto the cortex leads directly to tactile perception by examining whether it is independent from proprioceptive input by evaluating the impact of different hand postures on the perception of a tactile illusion across fingertips. Using the Cutaneous Rabbit Effect, a well studied illusion evoking the perception that a stimulus occurs at a location where none has been delivered, we found that hand posture has a significant effect on the perception of the illusion across the fingertips. This finding emphasizes that tactile perception arises from integration of perceived mechanical and proprioceptive input and not purely from tactile interaction with the external environment.     

Fluorescence spectroscopy in biochemistry: teaching basic principles with visual demonstrations

Although most biochemistry curricula include some treatment of light absorption and spectrophotometry, discussion of fluorescence spectroscopy is generally omitted. This omission is unfortunate given the increasing use of fluorescence in many fields of biochemical research. In this paper we briefly review the principles and applications of fluorescence in biochemical systems, from the viewpoint of teaching fluorescence in undergraduate curricula. Simple practical demonstrations are presented, which clearly demonstrate important concepts yet require minimal specialized equipment.