Synesthetic color experiences influence memory

We describe the extraordinary memory of C, a 21–year–old student who experiences synesthetic colors (i.e., photisms) when she sees, hears, or thinks of digits. Using three matrices of 50 digits, we tested C and 7 nonsynesthetes to evaluate whether C's synesthetic photisms influence her memory for digits. One matrix consisted of black digits, whereas the other two matrices consisted of digits that were either incongruent or congruent with the colors of C's photisms. C's recall of the incongruently colored digits was considerably poorer than her recall of either the black or the congruently colored digits. The 7 nonsynesthetes did not show such differences in their recall of the matrices. In addition, when immediate recall of the black digits was compared with delayed recall of those digits (48 hr), C showed no decrease in performance, whereas each of the nonsynesthetes showed a significant decrease. These findings both demonstrate C's extraordinary memory and show that her synesthetic photisms can influence her memory for digits.     

Immediate-early Fos protein levels in brainstem neurons of male and female gonadectomized mice subjected to cold exposure

The expression of the immediate early gene c-fos has been used extensively as a marker for neural activation in response to acute and chronic stressful stimuli in brain and spinal cord. The present study examined the expression of Fos protein in the brainstem nuclei of male and female gonadectomized mice in response to cold stress. Free-floating sections were processed immunohistochemically for Fos protein using standard avidin-biotin complex methods. The number of Fos-positive neurons in each nucleus was determined. Although the experiment was designed to look for gender differences, results were equivalent between females and males. After mice were exposed to a cold ambient temperature (4 degrees C) for 2 h, elevated numbers of Fos-positive neurons were counted in the medullary gigantocellular reticular nucleus, medullary raphe nucleus, nucleus of the solitary tract and in locus coeruleus. However, no elevated expression was found in nucleus ambiguus, nor in neurons of the A1 group, nor the C2 or C3 group. Similar to rats, these results with mice reveal a widespread arousal system in the lower brainstem activated by cold stress in both genders. These findings in gonadectomized mice have set the stage for investigations following hormonal and genetic manipulations.     

Glucocorticoid involvement in memory formation in a rat model for traumatic memory

Contextual fear conditioning under training conditions involving high stressor intensities has been proposed as an animal model for traumatic memories. The strength of memory for this task has been related to the intensity of the conditioning stressor and post-training corticosterone values. However, administration of a glucocorticoid receptor (GR) antagonist only attenuated memory for this task in rats conditioned at a moderate shock intensity (0.4 mA), but failed to influence conditioning in rats trained at a high shock intensity (1 mA). Here, we further questioned whether interfering with glucocorticoid action at the time of training might be effective in influencing contextual fear conditioning in rats trained under different shock intensities. Rats were subcutaneously injected with the glucocorticoid synthesis inhibitor metyrapone (50, 100 mg/kg) 90 min before being trained in the contextual fear conditioning task, at either 0.4 or 1 mA shock intensities. The results showed that metyrapone, in a dose-dependent manner: (i) attenuated long-term expression of contextual fear conditioning, both in 0.4- and 1 mA-trained rats; and (ii) efficiently prevented increased plasma corticosterone concentration. In addition to further supporting a facilitating role of glucocorticoids in memory consolidation, these findings suggest a critical involvement of these hormones in the formation of traumatic memories.     

Plasticity of the human auditory cortex induced by discrimination learning of non-native,mora-timed contrasts of the Japanese language

In this magnetoencephalographic (MEG) study, we examined with high temporal resolution the traces of learning in the speech-dominant left-hemispheric auditory cortex as a function of newly trained mora-timing. In Japanese, the “mora” is a temporal unit that divides words into almost isochronous segments (e.g., na-ka-mu-ra and to-o-kyo-o each comprises four mora). Changes in the brain responses of a group of German and Japanese subjects to differences in the mora structure of Japanese words were compared. German subjects performed a discrimination training in 10 sessions of 1.5 h each day. They learned to discriminate Japanese pairs of words (in a consonant, anni–ani; and a vowel, kiyo–kyo, condition), where the second word was shortened by one mora in eight steps of 15 msec each. A significant increase in learning performance, as reflected by behavioral measures, was observed, accompanied by a significant increase of the amplitude of the Mismatch Negativity Field (MMF). The German subjects' hit rate for detecting durational deviants increased by up to 35%. Reaction times and MMF latencies decreased significantly across training sessions. Japanese subjects showed a more sensitive MMF to smaller differences. Thus, even in young adults, perceptual learning of non-native mora-timing occurs rapidly and deeply. The enhanced behavioral and neurophysiological sensitivity found after training indicates a strong relationship between learning and (plastic) changes in the cortical substrate.     

A crossmodal attentional blink between vision and touch

There is currently a great deal of interest regarding the possible existence of a crossmodal attentional blink (AB) between audition and vision. The majority of evidence now suggests that no such crossmodal deficit exists unless a task switch is introduced. We report two experiments designed to investigate the existence of a crossmodal AB between vision and touch. Two masked targets were presented successively at variable interstimulus intervals. Participants had to respond either to both targets (experimental condition) or to just the second target (control condition). In Experiment 1, the order of target modality was blocked, and an AB was demonstrated when visual targets preceded tactile targets, but not when tactile targets preceded visual targets. In Experiment 2, target modality was mixed randomly, and a significant crossmodal AB was demonstrated in both directions between vision and touch. The contrast between our visuotactile results and those of previous audiovisual studies is discussed, as are the implications for current theories of the AB.     

A direct measure of facial similarity and its relation to human similarity perceptions

Research is reported on a measure of facial similarity in which the similarity of 2 faces is defined as the Euclidean distance between them in a principal-component space. Five studies were conducted in which participants rated sets of facial images, and in which the measure was applied to 2 problems in the eyewitness literature. Comparisons of ratings with distances derived from the principal-component analysis suggest that the measure corresponds reasonably well to perceptions of facial similarity. In addition, the measure correlates strongly with empirical measures of lineup fairness and is related to eyewitness identification performance. Further potential applications include a software tool for constructing arrays of faces of varying similarity, and a software tool for reconstructing facial images from memory.