IS DIGIT SUPERIORITY INDISPENSABLE WITH REGARD TO SHORT TERM MEMORY SPAN?

It is known that digits have a positive effect on the performance of short term memory (STM) span and it is called the digit superiority effect. This study aims to examine the effect of familiar stimuli (digits, colors, digit names, color names, and words) on STM span. In order to measure STM capacity, a memory span task was used including the digit, word, and color span lists. 91 participants (44 female, 47 male) aged between 18-27 (M = 21,43, SD = 1.50) participated in the study that consisted of three different experiments. Results of Experiment 1 revealed that there was a significant difference between the digit name and word with regard to span size and total span. In Experiment 2 and 3, the main effect of familiar stimulus type on total span and span size was significant, and also the difference between all types of stimuli was significant (Experiment II, digit name>word=color name; Experiment III, digit>digit name>color name>color). The common result obtained from all experiments is that digits are superior with regard to STM span than other familiar stimuli types such as words, color names, colors. This study confirmed that digit superiority effect is indispensable on verbal and visual STM span. Keywords Digit superiority, short term memory, memory span

Awake suppression after brief exposure to a familiar stimulus

Newly learned information undergoes a process of awake reactivation shortly after the learning offset and we recently demonstrated that this effect can be observed as early as area V1. However, reactivating all experiences can be wasteful and unnecessary, especially for familiar stimuli. Therefore, here we tested whether awake reactivation occurs differentially for new and familiar stimuli. Subjects completed a brief visual task on a stimulus that was either novel or highly familiar due to extensive prior training on it. Replicating our previous results, we found that awake reactivation occurred in V1 for the novel stimulus. On the other hand, brief exposure to the familiar stimulus led to ‘awake suppression’ such that neural activity patterns immediately after exposure to the familiar stimulus diverged from the patterns associated with that stimulus. Further, awake reactivation was observed selectively in V1, whereas awake suppression had similar strength across areas V1–V3. These results are consistent with the presence of a competition between local awake reactivation and top-down awake suppression, with suppression becoming dominant for familiar stimuli.

High frequency visual stimulation primes gamma oscillations for visually-evoked phase reset and enhances spatial acuity

The temporal frequency of sensory stimulation is a decisive factor in the plasticity of perceptual detection thresholds. However, surprisingly little is known about how distinct temporal parameters of sensory input differentially recruit activity of neuronal circuits in sensory cortices. Here we demonstrate that brief repetitive visual stimulation induces long-term plasticity of visual responses revealed 24 hours after stimulation, and that the location and generalization of visual response plasticity is determined by the temporal frequency of the visual stimulation. Brief repetitive low frequency stimulation (LFS, 2 Hz) is sufficient to induce a visual response potentiation that is expressed exclusively in visual cortex layer 4 and in response to a familiar stimulus. In contrast, brief, repetitive high frequency stimulation (HFS, 20 Hz) is sufficient to induce a visual response potentiation that is expressed in all cortical layers and transfers to novel stimuli. HFS induces a long-term suppression of the activity of fast-spiking interneurons and primes ongoing gamma oscillatory rhythms for phase-reset by subsequent visual stimulation. This novel form of generalized visual response enhancement induced by HFS is paralleled by an increase in visual acuity, measured as improved performance in a visual detection task.

Learning and motor-impulse control in domestic fowl and crows

Cognitive abilities allow animals to navigate through complex, fluctuating environments. For example, behavioural flexibility, which is the ability of an animal to alter their behaviour in response to a novel stimulus or to modify responses to as familiar stimulus or behavioural inhibition, defined as the ability to control a response in order to choose a conflicting course of action. Behavioural flexibility and inhibitory control are expected to vary between and within species based on socio-ecological factors. In the present study we compared performance of a captive group of eight crows, Corvus corone, and ten domestic fowl, Gallus gallus domesticus, in two cognitive tasks, the cylinder task as a test of motor inhibitory control, and reversal learning as a measure of learning ability and behavioural flexibility. Four crows and nine fowl completed the cylinder task, eight crows completed the reversal learning experiment and nine fowl were tested in the acquisition phase, however three fowl did not complete the reversal phase of the experiment due to time constraints. Crows performed significantly better in the cylinder task compared to domestic fowl. In the reversal learning experiment, species did not significantly differ in the number of trials until learning criterion was reached. In crows, individuals who needed less trials to reach learning criterion in the acquisition phase also needed less trials to reach the criterion in the reversal phase. This relationship was lacking in domestic fowl. Performance in the learning task did not correlate with performance in the cylinder task in domestic fowl. Our results show crows to possess significantly better motor-inhibitory control compared to domestic fowl, which could be indicative of this specific aspect of executive functioning to be lacking in domestic fowl. In contrast learning performance in a reversal learning task did not differ between crows and domestic fowl, indicating similar levels of behavioural flexibility in both species.

High frequency visual stimulation primes gamma oscillations for visually-evoked phase reset and enhances spatial acuity

The temporal frequency of sensory stimulation is a decisive factor in the bidirectional plasticity of perceptual detection thresholds. However, surprisingly little is known about how distinct temporal parameters of sensory input differentially impact neuronal, circuit, and perceptual function. Here we demonstrate that brief repetitive visual stimulation is sufficient to induce long-term plasticity of visual responses, with the temporal frequency of the visual stimulus determining the location and generalization of visual response plasticity. Brief repetitive low frequency stimulation (LFS, 2 Hz) is sufficient to induce a visual response potentiation that is exclusively expressed in layer 4 in response to the familiar stimulus. In contrast, brief, repetitive high frequency stimulation (HFS, 20 Hz) suppresses the activity of fast-spiking interneurons and primes ongoing gamma oscillatory rhythms for visually-evoked phase reset. Accordingly, visual stimulation subsequent to HFS induces non-stimulus specific visual response plasticity that is expressed in all cortical layers. The generalized visual response enhancement induced by HFS is paralleled by an increase in visual acuity measured by improved performance in a visual detection task.

Contextual experience modifies functional connectome indices of topological strength and organization

ABSTRACTStimuli presented at short temporal delays before functional magnetic resonance imaging (fMRI) can have a robust impact on the organization of synchronous activity in resting state networks. This presents an opportunity to investigate how sensory, affective and cognitive stimuli alter functional connectivity in rodent models. In the present study, we assessed the effect of a familiar contextual stimulus presented 10 minutes prior to sedation for imaging on functional connectivity. A subset of animals were co-presented with an unfamiliar social stimulus in the same environment to further investigate the effect of familiarity on network topology. Female and male rats were imaged at 11.1 Tesla and graph theory analysis was applied to matrices generated from seed-based functional connectivity data sets with 144 brain regions (nodes) and 10,152 pairwise correlations (edges). Our results show an unconventional network topology in response to the familiar (context) but not the unfamiliar (social) stimulus. The familiar stimulus strongly reduced network strength, global efficiency, and altered the location of the highest eigenvector centrality nodes from cortex to the hypothalamus. We did not observe changes in modular organization, nodal cartographic assignments, assortative mixing, rich club organization, and network resilience. The results suggest that experiential factors, perhaps involving associative or episodic memory, can exert a dramatic effect on functional network strength and efficiency when presented at a short temporal delay before imaging.

Experience shapes activity dynamics and stimulus coding of VIP inhibitory and excitatory cells in visual cortex

ABSTRACTCortical circuits are flexible and can change with experience and learning. However, the effects of experience on specific cell types, including distinct inhibitory types, are not well understood. Here we investigated how excitatory and VIP inhibitory cells in layer 2/3 of mouse visual cortex were impacted by visual experience in the context of a behavioral task. Mice learned to perform an image change detection task with a set of eight natural scene images, viewing these images thousands of times. Subsequently, during 2-photon imaging experiments, mice performed the task with these familiar images and three additional sets of novel images. Novel images evoked stronger overall activity in both excitatory and VIP populations, and familiar images were more sparsely coded by excitatory cells. The temporal dynamics of VIP activity differed markedly between novel and familiar images: VIP cells were stimulus-driven by novel images but displayed ramping activity during the inter-stimulus interval for familiar images. Moreover, when a familiar stimulus was omitted from an expected sequence, VIP cells showed extended ramping activity until the subsequent image presentation. This prominent shift in response dynamics suggests that VIP cells may adopt different modes of processing during familiar versus novel conditions.HIGHLIGHTSExperience with natural images in a change detection task reduces overall activity of cortical excitatory and VIP inhibitory cellsEncoding of natural images is sharpened with experience in excitatory neuronsVIP cells are stimulus-driven by novel images but show pre-stimulus ramping for familiar imagesVIP cells show strong ramping activity during the omission of an expected stimulus

Impaired expected value computations in schizophrenia are associated with a reduced ability to integrate reward probability and magnitude of recent outcomes

ABSTRACTBackgroundMotivational deficits in people with schizophrenia (PSZ) are associated with an inability to integrate the magnitude and probability of previous outcomes. The mechanisms that underlie probability-magnitude integration deficits, however, are poorly understood. We hypothesized that increased reliance on “value-less” stimulus-response associations, in lieu of expected value (EV)-based learning, could drive probability-magnitude integration deficits in PSZ with motivational deficits.MethodsHealthy volunteers (n= 38) and PSZ (n=49) completed a reinforcement learning paradigm consisting of four stimulus pairs. Reward magnitude (3/2/1/0 points) and probability (90%/80%/20%/10%) together determined each stimulus’ EV. Following a learning phase, new and familiar stimulus pairings were presented. Participants were asked to select stimuli with the highest reward value.ResultsPSZ with high motivational deficits made increasingly less optimal choices as the difference in reward value (probability*magnitude) between two competing stimuli increased. Using a previously-validated computational hybrid model, PSZ relied less on EV (“Q-learning”) and more on stimulus-response learning (“actor-critic”), which correlated with SANS motivational deficit severity. PSZ specifically failed to represent reward magnitude, consistent with model demonstrations showing that response tendencies in the actor-critic were preferentially driven by reward probability. ConclusionsProbability-magnitude deficits in PSZ with motivational deficits arise from underutilization of EV in favor of reliance on value-less stimulus-response associations. Consistent with previous work and confirmed by our computational hybrid framework, probability-magnitude integration deficits were driven specifically by a failure to represent reward magnitude. This work reconfirms the importance of decreased Q-learning/increased actor-critic-type learning as an explanatory framework for a range of EV deficits in PSZ.

Sameness May Be a Natural Concept That Does Not Require Learning

It has been assumed that when pigeons learn how to match to sample, they learn simple stimulus-response chains but not the concept of sameness. However, transfer to novel stimuli has been influenced by pigeons’ tendency to be neophobic. We trained pigeons on matching ( n = 7) and mismatching ( n = 8) with colors as samples and, with each sample, one color as the nonmatching comparison. We then replaced either the matching or the nonmatching stimulus with a familiar stimulus never presented with that sample. Results suggest that for both matching and mismatching, pigeons locate the stimulus that matches the sample: If the task involves matching, they chose it; if it involves mismatching, they avoid it. Thus, the concept of sameness is the basis for correct choice with both tasks. This finding suggests that sameness is a basic concept that does not have to be learned and may have evolved in many species, including humans.

An Conventional Methodology for Brain Finger Printing

Brain fingerprinting is based on finding that the brain generates a unique brain wave pattern when a person encounters a familiar stimulus use of functional magnetic resonance imaging in lie detection derives from studies suggesting that persons asked to lie show different patterns of brain activity than they do when being truthful. Issues related to the use of such evidence in courts are discussed. In the field of criminology, a new lie detector has been developed in the United States of America.This invention is supposed to be the best lie detector available as on date and is said to detect even smooth criminals who pass the polygraph test (the conventional lie detector test) with ease. The new method employs brain waves which are, useful in detecting whether the person subjected to the test, remembers finer details of crime. According to the experts, even if the person willingly suppresses the necessary information, the brain wave is sure to trap him.