Aversive learning enhances perceptual and cortical discrimination of indiscriminable odor cues

Learning to associate sensory cues with threats is critical for minimizing aversive experience. The ecological benefit of associative learning relies on accurate perception of predictive cues, but how aversive learning enhances perceptual acuity of sensory signals, particularly in humans, is unclear. We combined multivariate functional magnetic resonance imaging with olfactory psychophysics to show that initially indistinguishable odor enantiomers (mirror-image molecules) become discriminable after aversive conditioning, paralleling the spatial divergence of ensemble activity patterns in primary olfactory (piriform) cortex. Our findings indicate that aversive learning induces piriform plasticity with corresponding gains in odor enantiomer discrimination, underscoring the capacity of fear conditioning to update perceptual representation of predictive cues, over and above its well-recognized role in the acquisition of conditioned responses. That completely indiscriminable sensations can be transformed into discriminable percepts further accentuates the potency of associative learning to enhance sensory cue perception and support adaptive behavior.     

Schema-dependent gene activation and memory encoding in neocortex

When new learning occurs against the background of established prior knowledge, relevant new information can be assimilated into a schema and thereby expand the knowledge base. An animal model of this important component of memory consolidation reveals that systems memory consolidation can be very fast. In experiments with rats, we found that the hippocampal-dependent learning of new paired associates is associated with a striking up-regulation of immediate early genes in the prelimbic region of the medial prefrontal cortex, and that pharmacological interventions targeted at that area can prevent both new learning and the recall of remotely and even recently consolidated information. These findings challenge the concept of distinct fast (hippocampal) and slow (cortical) learning systems, and shed new light on the neural mechanisms of memory assimilation into schemas.     

Time-dependent central compensatory mechanisms of finger dexterity after spinal cord injury

Transection of the direct cortico-motoneuronal pathway at the mid-cervical segment of the spinal cord in the macaque monkey results in a transient impairment of finger movements. Finger dexterity recovers within a few months. Combined brain imaging and reversible pharmacological inactivation of motor cortical regions suggest that the recovery involves the bilateral primary motor cortex during the early recovery stage and more extensive regions of the contralesional primary motor cortex and bilateral premotor cortex during the late recovery stage. These changes in the activation pattern of frontal motor-related areas represent an adaptive strategy for functional compensation after spinal cord injury.     

Perceived number and evoked cortical potentials

Evoked cortical potentials and the numsber of flashes perceived were compared when subjects were presented with short trains of flashes under conditions where each presented flash could not be counted individually, but the train of flashes appeared to be flickering (1 to 14 flashes at 33.3 flashes per second). The rate at which each successive perceived flash was added appeared to correspond with the rate at which the successive components of the evoked response pattern were added. The temporal nature of this pattern was similar for both single flashes and trains of flashes. The results suggest that the onset of stimulation triggers a process whlich has a marked effect on both the cortical and perceptual response to subsequent stimulation.     

Is face processing species-specific during the first year of life?

Between 6 and 10 months of age, the infant's ability to discriminate among native speech sounds improves, whereas the same ability to discriminate among foreign speech sounds decreases. Our study aimed to determine whether this perceptual narrowing is unique to language or might also apply to face processing. We tested discrimination of human and monkey faces by 6-month-olds, 9-month-olds, and adults, using the visual paired-comparison procedure. Only the youngest group showed discrimination between individuals of both species; older infants and adults only showed evidence of discrimination of their own species. These results suggest that the "perceptual narrowing" phenomenon may represent a more general change in neural networks involved in early cognition.     

Cerebellum activation associated with performance change but not motor learning

The issue of whether the cerebellum contributes to motor skill learning is controversial, principally because of the difficulty of separating the effects of motor learning from changes in performance. We performed a functional magnetic resonance imaging investigation during an implicit, motor sequence-learning task that was designed to separate these two processes. During the sequence-encoding phase, human participants performed a concurrent distractor task that served to suppress the performance changes associated with learning. Upon removal of the distractor, participants showed evidence of having learned. No cerebellar activation was associated with the learning phase, despite extensive involvement of other cortical and subcortical regions. There was, however, significant cerebellar activation during the expression of learning; thus, the cerebellum does not contribute to learning of the motor skill itself but is engaged primarily in the modification of performance.     

Segregation of form, color, movement, and depth: anatomy, physiology, and perception

Anatomical and physiological observations in monkeys indicate that the primate visual system consists of several separate and independent subdivisions that analyze different aspects of the same retinal image: cells in cortical visual areas 1 and 2 and higher visual areas are segregated into three interdigitating subdivisions that differ in their selectivity for color, stereopsis, movement, and orientation. The pathways selective for form and color seem to be derived mainly from the parvocellular geniculate subdivisions, the depth- and movement-selective components from the magnocellular. At lower levels, in the retina and in the geniculate, cells in these two subdivisions differ in their color selectivity, contrast sensitivity, temporal properties, and spatial resolution. These major differences in the properties of cells at lower levels in each of the subdivisions led to the prediction that different visual functions, such as color, depth, movement, and form perception, should exhibit corresponding differences. Human perceptual experiments are remarkably consistent with these predictions. Moreover, perceptual experiments can be designed to ask which subdivisions of the system are responsible for particular visual abilities, such as figure/ground discrimination or perception of depth from perspective or relative movement--functions that might be difficult to deduce from single-cell response properties.     

Afterimage of perceptually filled-in surface

An afterimage induced by prior adaptation to a visual stimulus is believed to be due to bleaching of photochemical pigments or neural adaptation in the retina. We report a type of afterimage that appears to require cortical adaptation. Fixating a neon-color spreading configuration led not only to negative afterimages corresponding to the inducers (local afterimages), but also to one corresponding to the perceptually filled-in surface during adaptation (global afterimage). These afterimages were mutually exclusive, undergoing monocular rivalry. The strength of the global afterimage correlated to a greater extent with perceptual filling-in during adaptation than with the strength of the local afterimages. Thus, global afterimages are not merely by-products of local afterimages, but involve adaptation at a cortical representation of surface.     

Brain blood flow: alteration by prior exposure to a learned task

Chicks with the eyelids of one eye sutured were trained to discriminate between grains and pebbles. The learned experience was completely recognizable by the naive eye that had been occluded during training. When both eyes were opened after monocular training, the velocity of blood flow through paired left and right brain regions was identical. However, when chicks were reexposed to the discrimination situation, blood flow through the cerebral hemisphere associated with the naive eye was greater than that through the hemisphere associated with the trained eye.     

Temporal lobe lesions and perception of species-specific vocalizations by macaques

Japanese macaques were trained to discriminate two forms of their coo vocalization before and after unilateral and bilateral ablation of the temporal cortex. Unilateral ablation of the left superior temporal gyrus, including auditory cortex, resulted in an initial impairment in the discrimination, but similar unilateral ablation of the right superior temporal gyrus had no effect. Bilateral temporal lesions including auditory cortex completely abolished the ability of the animals to discriminate their coos. Neither unilateral nor bilateral ablation of cortex dorsal to and sparing the auditory cortex had any effect on the discrimination. The perception of species-specific vocalizations by Japanese macaques seems to be mediated by the temporal cortex, with the left hemisphere playing a predominant role.     

CORTICAL EVOKED POTENTIALS AND PERCEPTION OF PAIRED FLASHES

Digital computer techniques have been employed to extract cortical evoked potentials to paired visual stimuli. Changes in the evoked potentials have been related to perceptual phenomena varying as a function of the interval between flashes. Evoked potentials to paired stimuli, which gave rise to perceptual interactions, could be approximated by algebraic summation of the responses to the stimuli when presented separately.     

Errorless discrimination learning inthe pigeon: effects of chlorpromazine and impiramine

Chlorpromazine or imipramine disrupts a pigeon's performance on a discrimination between a vertical and horizontal line only if the discrimination was learned with errors. Errorless learning is obtained if training starts with an easy-to-learn discrimination of color and shifts progressively to the more difficult horizontal-vertical discrimination.     

Language discrimination by human newborns and by cotton-top tamarin monkeys

Humans, but no other animal, make meaningful use of spoken language. What is unclear, however, is whether this capacity depends on a unique constellation of perceptual and neurobiological mechanisms or whether a subset of such mechanisms is shared with other organisms. To explore this problem, parallel experiments were conducted on human newborns and cotton-top tamarin monkeys to assess their ability to discriminate unfamiliar languages. A habituation-dishabituation procedure was used to show that human newborns and tamarins can discriminate sentences from Dutch and Japanese but not if the sentences are played backward. Moreover, the cues for discrimination are not present in backward speech. This suggests that the human newborns' tuning to certain properties of speech relies on general processes of the primate auditory system.     

支持负载理论的新证据——基于斯特鲁普效应的研究

采用斯特鲁普任务范式,检验知觉负载理论是否适用于斯特鲁普效应,研究发现:屏幕中同时呈现6个彩色的颜色词,被试只对红色或者绿色的颜色词命名.在实验一中,需要在6个颜色词中进行视觉搜索(高负载),斯特鲁普效应消失了;在实验二中,增加有效线索,将注意直接集中在目标刺激上(低负载),产生了斯特鲁普效应.证明知觉负载理论也适用于斯特鲁普效应.     

The predictive value of changes in effective connectivity for human learning

During learning, neural responses decrease over repeated exposure to identical stimuli. This repetition suppression is thought to reflect a progressive optimization of neuronal responses elicited by the task. Functional magnetic resonance imaging was used to study the neural basis of associative learning of visual objects and their locations. As expected, activation in specialized cortical areas decreased with time. However, with path analysis it was shown that, in parallel to this adaptation, increases in effective connectivity occurred between distinct cortical systems specialized for spatial and object processing. The time course of these plastic changes was highly correlated with individual learning performance, suggesting that interactions between brain areas underlie associative learning.     

The Relative Operating Characteristic in Psychology: A technique for isolating effects of response bias finds wide use in the study of perception and cognition

The clinician looking, listening, or feeling for signs of a disease may far prefer a false alarm to a miss, particularly if the disease is serious and contagious. On the other hand, he may believe that the available therapy is marginally effective, expensive, and debilitating. The pilot seeing the landing lights only when they are a few yards away may decide that his plane is adequately aligned with the runway if he is alone and familiar with that plight. He may be more inclined to circle the field before another try at landing if he has many passengers and recent memory of another plane crashing under those circumstances. The Food and Drug administrator suspecting botulism in a canned food may not want to accept even a remote threat to the public health. But he may be less clearly biased if a recent false alarm has cost a canning company millions of dollars and left some damaged reputations. The making of almost any fine discrimination is beset with such considerations of probability and utility, which are extraneous and potentially confounding when one is attempting to measure the acuity of discrimination per se. The ROC is an analytical technique, with origins in statistical decision theory and electronic detection theory, that quite effectively isolates the effects of the observer's response bias, or decision criterion, in the study of discrimination behavior. This capability, pursued through a century of psychological testing, provides a relatively pure measure of the discriminability of different stimuli and of the capacity of organisms to discriminate. The ROC also treats quantitatively the response, or decision, aspects of choice behavior. The decision parameter can then be functionally related to the probabilities of the stimulus alternatives and to the utilities of the various stimulus-response pairs, or to the observer's expectations and motivations. In separating and quantifying discrimination and decision processes, the ROC promises a more reliable and valid solution to some practical problems and enhances our understanding of the perceptual and cognitive phenomena that depend directly on these fundamental processes. In several problem areas in psychology, effects that were supposed to reflect properties of the discrimination process have been shown by the ROC analysis to reflect instead properties of the decision process.     

Early eocene bat from wyoming

A fossil skeleton of an early Eocene bat, the oldest known flying mammal, was found in southwest Wyoming. The bat is assigned to the new species Icaronycteris index of the suborder Microchiroptera. It was apparently of a young male whose body was buried in varved marls of the Green River Formation, on the bottom of Fossil Lake, about 50 million years ago. The bones, some as slender as a human hair, show a few "primitive" characteristics such as a clawed index finger and a complete phalangeal formula, but the bat was fully developed -an anatomically precocious contemporary of the dog-sized polydactylous horse.     

Orbitofrontal dysfunction in patients with obsessive-compulsive disorder and their unaffected relatives

Obsessive-compulsive disorder (OCD) is characterized by repetitive thoughts and behaviors associated with underlying dysregulation of frontostriatal circuitry. Central to neurobiological models of OCD is the orbitofrontal cortex, a neural region that facilitates behavioral flexibility after negative feedback (reversal learning). We identified abnormally reduced activation of several cortical regions, including the lateral orbitofrontal cortex, during reversal learning in OCD patients and their clinically unaffected close relatives, supporting the existence of an underlying previously undiscovered endophenotype for this disorder.     

采用双任务范式使被试将工作记忆信息保存在工作记忆当中并完成选择性注意任务,结果发现:视觉空间工作记忆负荷不能使熟悉面孔的干扰效应消失,语义工作记忆负荷使熟悉面孔的干扰效应在高知觉负荷条件下消失.因此,熟悉面孔在高知觉负荷条件下可能是以语义的方式存储在工作记忆当中,在低知觉负荷条件下可能是同时存储在视觉空间工作记忆和语义工作记忆中.

采用双任务范式使被试将工作记忆信息保存在工作记忆当中并完成选择性注意任务,结果发现:视觉空间工作记忆负荷不能使熟悉面孔的干扰效应消失,语义工作记忆负荷使熟悉面孔的干扰效应在高知觉负荷条件下消失.因此,熟悉面孔在高知觉负荷条件下可能是以语义的方式存储在工作记忆当中,在低知觉负荷条件下可能是同时存储在视觉空间工作记忆和语义工作记忆中.