Cajal in Barcelona: From yesterday to today, from the neuron to the network

The synaptic and network theories of memory, which Cajal first advanced in Barcelona around 1890, have been firmly established and elaborated by three generations of neuroscientists. This article outlines a corollary model of memory in the cerebral cortex that derives from those theories and is empirically supported by modern functional methods. The model posits that the elementary unit of memory or knowledge is a network of neurons of the cerebral cortex associated by life experience according to Hebbian principles of synaptic modulation (a cognit). Networks or cognits of perceptual memory are hierarchically organized and distributed in posterior association cortex; those of executive memory, also hierarchically organized, are distributed in frontal association cortex. In the course of goal-directed behavior and language, perceptual and executive cognits engage in the perception-action cycle, the cybernetic cycle that dynamically links the cortical cognitive networks with the environment in the pursuit of goals,. The prefrontal cortex, at the summit of that cycle, and interacting with cortical and subcortical structures, guides behavior and language to their goals by means of its executive functions of planning, executive attention, working memory, decision-making, and inhibitory control

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Linking perceptual learning with identical stimuli to imagery perceptual learning.

Perceptual learning is usually thought to be exclusively driven by the stimuli presented during training (and the underlying synaptic learning rules). In some way, we are slaves of our visual experiences. However, learning can occur even when no stimuli are presented at all. For example, Gabor contrast detection improves when only a blank screen is presented and observers are asked to imagine Gabor patches. Likewise, performance improves when observers are asked to imagine the nonexisting central line of a bisection stimulus to be offset either to the right or left. Hence, performance can improve without stimulus presentation. As shown in the auditory domain, performance can also improve when the very same stimulus is presented in all learning trials and observers were asked to discriminate differences which do not exist (observers were not told about the set up). Classic models of perceptual learning cannot handle these situations since they need proper stimulus presentation, i.e., variance in the stimuli, such as a left versus right offset in the bisection stimulus. Here, we show that perceptual learning with identical stimuli occurs in the visual domain, too. Second, we linked the two paradigms by telling observers that only the very same bisection stimulus was presented in all trials and asked them to imagine the central line to be offset either to the left or right. As in imagery learning, performance improved.

Effects of exposure to food images on physiological reactivity and emotional responses in women with bulimia nervosa / Efecto de la exposición a imágenes de comida sobre la reactividad psicofisiológica y las reacciones emocionales en mujeres con bulimia nerviosa

Background: The aim of this study is to compare the effectiveness of two exposure procedures on habituation of emotional responses to food stimuli: (a) exposure to external cues (food images) without eating forbidden food (CE) and (b) exposure to external cues eating forbidden food (with purge prevention). The influence of craving-trait and mood state on the habituation process is also studied. Method: Emotional modulation of the defense startle reflex was assessed in 26 women at risk of bulimia nervosa. After four exposure trials, changes in the following variables were measured: (a) food craving-state; (b) physiological measures: hearth rate (HR) and skin conductance response (SCR); (c) motivational patterns towards food (defense startle response); and (d) valence, arousal and dominance of the emotional response to food images. Results: After treatment, subjects tended to show non-significant lower SCR and heart orientation responses (vs. defense responses); defense startle response was also significantly lower. Conclusions: The exposure procedure, the induced emotional state and the number of exposure trials are analyzed (AU)

Antecedentes: en este estudio comparamos la eficacia de dos procedimientos de exposición sobre la habituación de reacciones emocionales a alimentos: a) claves externas (imágenes de comida) sin ingerir alimentos prohibidos, y b) claves externas en personas que sí los han ingerido (impidiendo que se produzca el vómito). Además consideramos la influencia de la intensidad del craving rasgo y del estado de ánimo. Evaluamos la modulación emocional del reflejo defensivo de sobresalto motor (RMS) en 26 mujeres con riesgo de padecer bulimia nerviosa. Método: tras cuatro bloques de exposición, se midieron los cambios en: a) craving estado por la comida; b) tasa cardíaca (TC) y respuesta electrodérmica de conductancia (SCR); c) patrones motivacionales ante la comida (RMS); y d) estimaciones afectivas de valencia, arousal y dominancia de las emociones producidas por las imágenes de los alimentos. Resultados: como consecuencia del tratamiento los sujetos tendían a mostrar de forma estadísticamente no significativa menores SCRs y una tendencia de cambio de patrón de respuesta de defensa cardíaca (RD) a respuesta de orientación (RO); sí se apreciaban diferencias significativas en RMS. Conclusiones: se comenta el papel desempeñado por el tipo de exposición utilizado, los estados emocionales inducidos y el número de ensayos de exposición (AU)

Reconocimiento falso y ansiedad estado/rasgo / False recognition and state/trait anxiety

En este estudio se analiza la relación entre la ansiedad estado/rasgo (STAI, State-Trait Anxiety Inventory) y el reconocimiento falso empleando el paradigma Deese/Roediger-McDermott (DRM). En este paradigma, los participantes estudian palabras altamente asociadas a una palabra crítica no presentada; posteriormente, en el test de reconocimiento la palabra crítica se reconoce falsamente. Se presentaron 10 listas de palabras a 161 participantes para estudiar las ilusiones asociativas de memoria. Los resultados mostraron que no existía correlación entre la ansiedad, ni en su modalidad estado ni en su modalidad rasgo, y el reconocimiento falso. Solamente encontramos la esperada correlación positiva entre ansiedad estado y ansiedad rasgo. Posteriormente, los datos obtenidos se analizaron teniendo en cuenta las puntuaciones extremas en ansiedad según el STAI. Así, se comparó el reconocimiento falso de los individuos con alta y baja ansiedad estado, por un lado, y con alta y baja ansiedad rasgo, por otro. De nuevo, los análisis indicaron que no existían diferencia en el nivel de reconocimiento falso ni entre los grupos de alta/baja ansiedad estado ni entre los grupos de alta/baja ansiedad rasgo. En conclusión, estos resultados sugieren que los individuos con alta ansiedad no son más susceptibles a producir ilusiones asociativas de memoria que los individuos con baja ansiedad(AU)

The present study analyzed the relationship between state/trait anxiety and false recognition using the Deese/Roediger-McDermott (DRM) paradigm. In this paradigm, participants study words that are highly associated with a non-presented critical lure; subsequently, when a memory test is administered, the critical lure is consistently recognized falsely. Ten 10-word DRM lists were presented to 161 participants to study associative memory illusions. The results showed no correlation between anxiety (either state or trait assessed using the State-Trait Anxiety Inventory; STAI) and false recognition. Only the expected positive correlation between state anxiety and trait anxiety was found. Thereafter, the results were analyzed according to extreme scores on the STAI. So, high state anxiety individuals were compared with low state anxiety individuals in false recognition, and the same was done with individuals with high versus low trait anxiety. Again, these detailed analyses revealed no differences on the level of false recognition, neither between high/low state anxiety nor between high/low trait anxiety. In conclusion, these findings suggest that individuals with high state anxiety and individuals with high trait anxiety were no more prone to produce associative illusions of memory than individuals with low state and trait anxiet(AU)

Shifting attention within memory representations involves early visual areas.

Prior studies have shown that spatial attention modulates early visual cortex retinotopically, resulting in enhanced processing of external perceptual representations. However, it is not clear whether the same visual areas are modulated when attention is focused on, and shifted within a working memory representation. In the current fMRI study participants were asked to memorize an array containing four stimuli. After a delay, participants were presented with a verbal cue instructing them to actively maintain the location of one of the stimuli in working memory. Additionally, on a number of trials a second verbal cue instructed participants to switch attention to the location of another stimulus within the memorized representation. Results of the study showed that changes in the BOLD pattern closely followed the locus of attention within the working memory representation. A decrease in BOLD-activity (V1-V3) was observed at ROIs coding a memory location when participants switched away from this location, whereas an increase was observed when participants switched towards this location. Continuous increased activity was obtained at the memorized location when participants did not switch. This study shows that shifting attention within memory representations activates the earliest parts of visual cortex (including V1) in a retinotopic fashion. We conclude that even in the absence of visual stimulation, early visual areas support shifting of attention within memorized representations, similar to when attention is shifted in the outside world. The relationship between visual working memory and visual mental imagery is discussed in light of the current findings.

[Internal reference frame for representation and storage of visual information during standing].

The participation of different afferent systems in organization of internal reference frame was studied. For this was chosen the task of visual comparison that executed in different experimental conditions: in upright standing, with inclined body or head in frontal plane and availability or non-availability visual information about external environment. Results showed that dominant orientation of referent stimulus (minimal value of mean error and minimal variability of responses) was connected with body position, mainly head position but not with gravity and visual vertical even when visual environment was available. It means that for creating the internal representing of vertical CNS mainly uses proprioceptive information about longitudinal axis of body.

Condicionamiento clásico electrodérmico aversivo y apetitivo utilizando imágenes como estímulos / Aversive and appetitive electrodermal classical conditioning using pictures as stimuli

El principal objetivo de este estudio consistió en comprobar si era posible obtener condicionamiento clásico electrodérmico, tanto aversivo como apetitivo, utilizando imágenes como estímulos condicionados (ECs) y estímulos incondicionados (EIs). Además, se pretendía averiguar si, como consecuencia de dicho condicionamiento, se observaba el fenómeno de disminución de la respuesta incondicionada (RI). Para ello se seleccionaron como estímulos imágenes del IAPS («International Affective Picture System»). Como EI aversivo (EIav) se empleó una fotografía que mostraba un rostro quemado y como EI apetitivo (EIap) una escena de contenido erótico. Tanto el EC aversivo (ECav) como el EC apetitivo (ECap) consistieron en fotografías con valores intermedios de valencia y arousal que mostraban rostros de varones. En el grupo experimental se presentaron 10 ensayos ECav/EIav y otros 10 ensayos ECap/EIap. En el grupo de control cada estímulo (ECav, ECap, EIav y EIap) se presentó en 10 ocasiones en orden pseudoaleatorio. Se registró la respuesta de conductancia electrodérmica (Skin Conductance Response, SCR) elicitada por los ECs y EIs. Los resultados mostraron que se había obtenido condicionamiento aversivo, aunque no apetitivo ni disminución de la RI. Se discuten las dificultades para obtener condicionamiento utilizando imágenes como estímulos y las posibles alternativas para superarlas en futuras investigaciones (AU)

The principal goal of this study was to verify whether it was possible to obtain both aversive and appetitive electrodermal classical conditioning, using pictures as conditioned stimuli (CS), and unconditioned stimuli (US). Additionally, we tried to verify whether, as a consequence of such conditioning, diminution of the unconditioned response (UR) was observed. With this aim, IAPS («International Affective Picture System») pictures were selected as stimuli. A picture showing a burnt face was used as the aversive US (USav), and a picture showing a scene with erotic content was used as the appetitive US (USap). As the aversive CS (CSav), and appetitive CS (CSap), two images with intermediate values of valence and arousal showing male faces were selected. In the experimental group, 10 CSav/USav and 10 CSap/ USap trials were presented. In the control group 10 CSav, CSap, USav, and USap trials were presented in pseudorandom order. Skin conductance response (SCR) elicited by both the CSs and the USs was scored. Results showed aversive conditioning, but neither appetitive conditioning nor UR diminution. Problems to obtain conditioning using pictures as stimuli and possible options to overcome them in future research are discussed (AU)

Visual field heterogeneity, laterality, and eidetic imagery in synesthesia.

JS was a grapheme-color synesthete in whom numerals and letters of the alphabet consistently evoked colors. In the first set of experiments we showed that the color - in a consistent and reliable manner - was most pronounced in the left visual field and in central vision. In the second experiment we devised a novel test for eidetic imagery and showed that his self-report of enhanced imagery could be verified experimentally. The implications of these findings for the level at which synesthesia occurs, the 'enhanced cross-activation' model, and the mechanisms of visual memory are discussed.

Time gaps in mental imagery introduced by competing saccadic tasks.

Recently it has been suggested that, somehow similarly to visual saccadic suppression, saccades interrupt some mental activities. After demonstrating that spontaneous eye movements can be used to trace the instantaneous evolution of mental imagery, we show here that making a voluntary saccade or anti-saccade as a secondary task introduces a large delay in a concurrent motion imagery task. An identical task requiring a shift of attention but not saccades also delays imagery, though to a lesser extent. The delay is never compensated afterwards, as if the time dedicated to the secondary task was lost. In contrast, motion imagery is not delayed by spontaneous saccades that accompany imagery, as compared to a fixation condition. We conclude that important time gaps in cognitive activity are introduced only by tasks competing for attentional resources, including voluntary saccades, in dual-task contexts.

Formation of cognitive structures in conditioned-reflex behavior in monkeys: Relationship with type of visual information.

The characteristics of learning processes and long-term memory (LTM) were studied in rhesus macaques discriminating visual stimuli (geometrical figures of different shapes, sizes, and orientations, and with different spatial relationships between image components). Trained monkeys were tested for the ability to perform invariant recognition after stimulus transformation, i.e., changes in size, shape, number of objects, and spatial relationships. Analysis of behavioral characteristics (correct solutions, refusals to decide, motor response times) revealed differences associated with the type of visual information. When monkeys discriminated between black and white geometrical figures of different shapes and orientations, as well as black-and-white figures with different shapes or orientations, the learning time was short and transformation of the stimuli had no effect on correct solutions: there was complete transfer of learning. When monkeys discriminated figures of different sizes or complex images with different spatial relationships, the learning time was significantly greater. Changes in the size and shape of figures led to significant reductions in correct solutions and significant increases in refusals to solve the task and in motor reaction times. Invariance of discrimination in this case appeared after additional training. The results obtained here showed that in conditioned reflex learning, the sensory processing of stimuli has the result that discriminatory features are formed in LTM, i.e., cognitive structures (functional neurophysiological mechanisms), these supporting the classification of visual images. The temporal conditioned link of the executive reaction is established with these. Their formation is determined by the type of sensory information and the existence in LTM of separate subsystems for spatial and non-spatial information.

Awareness of memory functioning, autobiographical memory and identity in early-stage dementia.

Sense of identity is thought to be closely related to autobiographical memory. Theoretical models of awareness suggest that both may also be related to level of awareness of memory functioning among people with early-stage dementia. This study explores the relationships between autobiographical memory, identity and awareness in early-stage dementia. Thirty participants with Alzheimer's disease, or vascular or mixed dementia were assessed using the Autobiographical Memory Interview, with an additional section eliciting recall for the mid-life period, the Tennessee Self-Concept Scale, and the Memory Awareness Rating Scale. Lower levels of awareness of memory functioning were associated with poorer autobiographical recall for the mid-life period and with a more positive and definite sense of identity. Reduced awareness may serve a protective function against the threats to self posed by the onset and progression of dementia.

[Forming of the visual cognitive structures in the monkey conditioned-reflex behaviour: the dependence on the sensory information].

In monkeys, changes in size and shape of figures led to a significant decrease of correct solutions in training and a considerable increase of refusals from solution of tasks as well as the time of their motor response. The invariance of differentiation in this case was achieved after additional training. The data obtained show that, based on the stimulus sensory processing in conditioned-reflex training, in the long-term memory some differentiating signs are formed: the cognitive structures (the functional neurophysiological mechanisms) maintaining the classification of visual images. With these structures, temporary conditioned connection will be established. Their formation will be determined by the type of sensory information and provided for by existence in the long-term memory of separate subsystems for spatial as well as non-spatial information.

Effect of a fatiguing protocol on motor imagery accuracy.

This study was devised to evaluate the influence of muscle fatigue on athletes' ability to perform motor imagery. Performance impairment is a consequence of fatigue, but alterations on perception and mental activity may also occur. To test whether peripheral fatigue affects mental processes, ten sports students imagined three consecutive countermovement jumps before and after a fatiguing protocol, through repetition of upright movements, at 70% of maximal voluntary contraction, until exhaustion. Autonomic nervous system responses and imagined movement durations were considered the dependent variables. Actual duration was systematically overestimated during both visual and kinesthetic imagery, but motor imagery duration and autonomic responses were similar without and under fatigue. Results suggest that muscle fatigue, unlike fatigue induced by prolonged exercise, does not elicit mental fatigue and therefore does not alter motor imagery accuracy.

Visual synaesthesia in the blind.

Synaesthesia is characterised by idiosyncratic ectopic sensations which commonly take the form of coloured visual impressions evoked by touch or hearing. We studied six late-blind individuals who have retained synaesthetic colour perception. Four of them had been without any form of genuine colour vision for more than 10 years. All perceived colours when they heard or thought about letters, numbers, and time-related words (days of the week and months of the year). One experienced synaesthetic colours for all words. Another saw Braille characters as coloured dots when he touched them. The aberrant experiences were compelling and reliable: detailed verbal descriptions of the colours were remarkably consistent in tests more than 2 months apart. The percepts predominantly took the form of coloured patches, localised in body-centred space for five of the subjects and in head-centred space for the sixth. This implies that the neural activity underlying synaesthesia occurs after the establishment of a visual representation independent of eye (or head) position. The synaesthetic colour depended only on phonetic cues in one case, but on semantic context in others. Although synaesthesia might be due to idiosyncratic, aberrant corticocortical connectivity established during early development, it can persist for very long periods with little or no natural experience in the referred modality and therefore does not depend solely on continuing associative learning.

Switching destinations: memory change in wood ants.

We have studied the changing use of spatial memories in wood ants by charting how the ants' paths transform when ants are first trained to feed at one site and must then switch to another site. Because ants, which are trained to approach a single feeding site from a single starting point, are attracted directly to that goal when started from unfamiliar positions, we describe the ants' paths in terms of the use of two stored snapshots. Each snapshot consists of retinotopic views of the ants' surroundings acquired at one of the two feeding sites. When a snapshot is activated, it draws an ant to the related site from a wide range of directions. Here, we focus on routes that occur before ants have learnt to go directly from the start to the second site. The initial direction of the ant's path is then mostly aimed either at the first site or between the two sites. On 62.2% of all recorded paths, this segment is followed by an abrupt turn, after which the ant often aims directly at the second feeding site. The details of this behaviour suggest that, after the turn, control of the path switches from the snapshot recorded at the first feeding site (or some combination of the two snapshots) to the snapshot recorded at the second feeding site. We discuss different ways in which control might be transferred from one snapshot to the other.

The binding and recall of snapshot memories in wood ants (Formica rufa L.).

Insects can locate spatial goals by means of 2-D retinotopic views of the surrounding landmarks, which they memorise from the vantage point of the goal. Wood ants acquire such snapshot memories while fixating conspicuous landmarks with frontal retina, and their snapshots extend horizontally at least 120 degrees into the periphery. Are spatially separate items within such an extended snapshot bound together so that a snapshot is recalled as a whole, or are its components recognised individually? We approached this question by training ants to find food midway between two upright black cylinders of different sizes and then examined where they searched when they were given two cylinders of the same size. If the ants know which cylinder replaces the small cylinder and which the large, they should search at a position where the two equal-sized cylinders subtend the same angles as do the training cylinders when viewed from the feeder. Ants conformed to this prediction under one condition, searching at a shorter distance from the substitute for the large cylinder than from the substitute for the small cylinder. But, under another condition, ants were unable to distinguish between the two equal-sized cylinders. Ants failed when white curtains completely surrounded the platform on which the cylinders were placed. They succeeded when one side of the platform had a patterned curtain. We suggest that ants take two snapshots at the feeding site, one when facing the small cylinder and one when facing the large cylinder, and that each snapshot includes the patterned curtain, if it is there. Ants will view the patterned curtain with the lateral retina of one eye when facing the small cylinder and with the lateral retina of the other eye when facing the large cylinder. Our data suggest that there may be associative links between these spatially separate components of the snapshot, which cause the memory of the small cylinder or the large cylinder to be recalled according to which eye sees the curtain. It seems that an extended snapshot not only enhances the accuracy of localisation but can also increase the reliability of snapshot recall, provided that the components of a snapshot are bound together.

Switching skills on by turning off part of the brain.

Snyder and Mitchell (1999) have argued that the extraordinary skills of savants, including mathematics and drawing, are within us all but cannot normally be accessed without some form of brain damage. It has also been argued that such skills can be made accessible to normal people by switching off part of their brain artificially using magnetic pulses (Carter, 1999). Using repetitive transcranial magnetic stimulation (rTMS) to interrupt the function of the frontotemporal lobe, a region of the brain implicated in the development of savant skills (Miller et al., 1996,1998), we tested this hypothesis. Here we show that savant-type skills improved in 5 out of 17 participants during the period of stimulation. The enhanced skills included declarative memory, drawing, mathematics, and calendar calculating. In addition to overall improvement being observed, striking improvements in individual performance on various tasks were also seen.

Power spectra and distribution of contrasts of natural images from different habitats.

Some theories for visual receptive fields postulate that they depend on the image statistics of the natural habitat. Consequently, different habitats may lead to different receptive fields. We thus decided to study how some of the most relevant statistics vary across habitats. In particular, atmospheric and underwater habitats were compared. For these habitats, we looked at two measures of the power spectrum and one of the distributions of contrasts. From power spectra, we analyzed the log-log slope of the fall and the degree of isotropy. From the distribution of contrasts, we analyzed the fall in a semi-log scale. Past studies found that the spatial power spectra of natural atmospheric images fall linearly in logarithmic axes with a slope of about -2 and that their distribution of contrasts shows an approximate linear fall in semi-logarithmic axes. Here, we show that the power spectrum of underwater images have statistically significantly steeper slopes ( approximately -2.5 in log-log axes) than atmospheric images. The vast majority of power spectra are non-isotropic, but their degree of anisotropy is extremely low, especially in atmospheric images. There are also statistical differences across habitats for the distribution of contrasts, with it falling faster for underwater images than for atmospheric ones. We will argue that these differences are due to the optical properties of water and that the differences have relevance for theories of visual receptive fields. These theories would predict larger receptive fields for aquatic animals compared to land animals.

EEG activity of aviators during imagery flight training.

OBJECTIVE: Imagery flight training (IFT) is widely used in aviation without neurophysiological evaluation. Electroencephalogram (EEG) during IFT was compared between experienced fighter pilots (FP) and novice pilots (NP). METHODS: Six FP and 9 NP performed imagery right bank, left bank, right roll, and left roll maneuvers. Each task was repeated 5 times in a random order. Instantaneous EEG power was calculated by the intertrial variance method. RESULTS: In FP, 3 waves of event-related desynchronization (ERD) were observed. The third ERD (ERD3) was observed at all the electrode positions except Fp1 which began 0.25 s before the beginning of IFT and reached its peak 0.25 s after the beginning of IFT. In NP, ERD was not related to the start of IFT. The difference in event-related EEG at the peak of ERD3 was not significant between FP and NP. However, the negative change to the peak of ERD3 was significantly larger in FP than in NP. CONCLUSIONS: It is speculated that ERD3 in FP may indicate the activation of cortical areas including visual- and motor-related areas involved in IFT. SIGNIFICANCE: It is speculated that the representation of IFT was programmed in visual- and motor-related cortical areas as an aviator's career advances.