Switcher-random-walks: a cognitive-inspired mechanism for network exploration

Semantic memory is the subsystem of human memory that stores knowledge of concepts or meanings, as opposed to life specific experiences. The organization of concepts within semantic memory can be understood as a semantic network, where the concepts (nodes) are associated (linked) to others depending on perceptions, similarities, etc. Lexical access is the complementary part of this system and allows the retrieval of such organized knowledge. While conceptual information is stored under certain underlying organization (and thus gives rise to a specific topology), it is crucial to have an accurate access to any of the information units, e.g. the concepts, for efficiently retrieving semantic information for real-time needings. An example of an information retrieval process occurs in verbal fluency tasks, and it is known to involve two different mechanisms: -clustering-, or generating words within a subcategory, and, when a subcategory is exhausted, -switching- to a new subcategory. We extended this approach to random-walking on a network (clustering) in combination to jumping (switching) to any node with certain probability and derived its analytical expression based on Markov chains. Results show that this dual mechanism contributes to optimize the exploration of different network models in terms of the mean first passage time. Additionally, this cognitive inspired dual mechanism opens a new framework to better understand and evaluate exploration, propagation and transport phenomena in other complex systems where switching-like phenomena are feasible.Comment: 9 pages, 3 figures. Accepted in "International Journal of Bifurcations and Chaos": Special issue on "Modelling and Computation on Complex Networks

Frequency of neurolopsychological deficits after traumatic brain injury

El traumatismo craneoencefálico (TCE) puede conllevar impactantes cambios en la vida cotidiana, que incluyen alteraciones a nivel social, profesional, comunicativo y cognitivo (dificultades atencionales, mnemónicas y ejecutivas). Este estudio tuvo por objeto caracterizar la ocurrencia de déficits neuropsicológicos post-TCE y constatar el impacto ocasionado por el nivel de severidad del trauma en el desempeño cognitivo de los pacientes. Participaron 96 adultos en la muestra total, que fue dividida en dos grupos para evaluar el nivel de severidad del trauma: TCE leve (n=39) y TCE grave (n=77). La gravedad de la lesión se clasificó por medio de la Escala de Coma de Glasgow, por la duración de la pérdida de consciencia, o por la amnesia post-traumática. No había diferencias entre la edad y la escolaridad de los participantes. Para la comparación entre los grupos en cuanto a la distribución de ocurrencia de déficits neuropsicológicos, se utilizó el Chi-cuadrado. Se utilizó una batería de evaluación neuropsicológica flexible conformada por tareas verbales y visoespaciales de habilidades lingüísticas, mnemónicas y ejecutivas. Los grupos no se diferenciaron en cuanto a las variables sociodemográficas. Los pacientes con TCE leve tuvieron mejores puntajes comparados con los de TCE grave (número de errores y categorías completadas del Test de clasificación de tarjetas de Wisconsin- [WCST, por sus siglas en inglés]; errores en la parte B del Test de Hayling; y en la interferencia retro y proactiva del Test de aprendizaje auditivo verbal de Rey [RAVLT, por sus siglas en inglés]. El nivel de severidad del trauma parece mostrar diferencias en los individuos en cuanto al desempeño en memoria episódica de información nueva y en el control de interferencia entre los recuerdos; lo mismo se aplica a las funciones de flexibilidad e inhibición. Estos resultados sugieren que es necesaria una mayor inversión en acciones de políticas públicas, priorizando intervenciones neurocognitivas reeducativas y métodos de prevención de accidentes relacionados con lesiones traumáticas que tengan alta incidencia de secuelas.El traumatismo craneoencefálico (TCE) puede conllevar impactantes cambios en la vida cotidiana, que incluyen alteraciones a nivel social, profesional, comunicativo y cognitivo (dificultades atencionales, mnemónicas y ejecutivas). Este estudio tuvo por objeto caracterizar la ocurrencia de déficits neuropsicológicos post-TCE y constatar el impacto ocasionado por el nivel de severidad del trauma en el desempeño cognitivo de los pacientes. Participaron 96 adultos en la muestra total, que fue dividida en dos grupos para evaluar el nivel de severidad del trauma: TCE leve (n=39) y TCE grave (n=77). La gravedad de la lesión se clasificó por medio de la Escala de Coma de Glasgow, por la duración de la pérdida de consciencia, o por la amnesia post-traumática. No había diferencias entre la edad y la escolaridad de los participantes. Para la comparación entre los grupos en cuanto a la distribución de ocurrencia de déficits neuropsicológicos, se utilizó el Chi-cuadrado. Se utilizó una batería de evaluación neuropsicológica flexible conformada por tareas verbales y visoespaciales de habilidades lingüísticas, mnemónicas y ejecutivas. Los grupos no se diferenciaron en cuanto a las variables sociodemográficas. Los pacientes con TCE leve tuvieron mejores puntajes comparados con los de TCE grave (número de errores y categorías completadas del Test de clasificación de tarjetas de Wisconsin- [WCST, por sus siglas en inglés]; errores en la parte B del Test de Hayling; y en la interferencia retro y proactiva del Test de aprendizaje auditivo verbal de Rey [RAVLT, por sus siglas en inglés]. El nivel de severidad del trauma parece mostrar diferencias en los individuos en cuanto al desempeño en memoria episódica de información nueva y en el control de interferencia entre los recuerdos; lo mismo se aplica a las funciones de flexibilidad e inhibición. Estos resultados sugieren que es necesaria una mayor inversión en acciones de políticas públicas, priorizando intervenciones neurocognitivas reeducativas y métodos de prevención de accidentes relacionados con lesiones traumáticas que tengan alta incidencia de secuelas.Traumatic brain injury (TBI) can lead to significant changes in daily life, as well as in social, labor, communicative, and cognitive domains (attention, memory and executive functions). This study aimed to characterize the occurrence of post-TBI neuropsychological deficits as well as to determine whether there is an impact related to the level of severity of the trauma on the patient's performance. Ninety-six adults participated in the study, who were divided in two groups to assess the trauma's level of severity: mild TBI (n=39) and severe TBI (n=57). This severity was classified by the Glasgow Coma Scale, by the duration of consciousness loss, or by post-traumatic amnesia. There were no differences between the groups regarding variables of age and years of schooling. A Chi- square test was used to do a comparison between the two groups in terms of occurrence of neuropsychological deficits. Verbal, visuospatial, mnemonic, linguistic and executive tests composed a flexible neuropsychological battery. Patients with mild TBI had better scores compared to those with severe TBI (number of errors and in completed categories of the Modified Wisconsin Card Sorting Test (MWCST); errors in Part B of The Hayling Test; and proactive and retroactive interference in the Rey Auditory Verbal Learning Test (RAVLT). The severity of the trauma seems to differentiate individual's performance on episodic memory of new information and in the control of interference between memories; the same is applied to flexibility and inhibition functions. These results suggest the need for more investments in public health policy actions, prioritizing neurocognitive remedial intervention and prevention methods for such condition with high incidence of sequelae

Age of second language acquisition affects nonverbal conflict processing in children : an fMRI study

Background: In their daily communication, bilinguals switch between two languages, a process that involves the selection of a target language and minimization of interference from a nontarget language. Previous studies have uncovered the neural structure in bilinguals and the activation patterns associated with performing verbal conflict tasks. One question that remains, however is whether this extra verbal switching affects brain function during nonverbal conflict tasks. Methods: In this study, we have used fMRI to investigate the impact of bilingualism in children performing two nonverbal tasks involving stimulus-stimulus and stimulus-response conflicts. Three groups of 8-11-year-old children - bilinguals from birth (2L1), second language learners (L2L), and a control group of monolinguals (1L1) - were scanned while performing a color Simon and a numerical Stroop task. Reaction times and accuracy were logged. Results: Compared to monolingual controls, bilingual children showed higher behavioral congruency effect of these tasks, which is matched by the recruitment of brain regions that are generally used in general cognitive control, language processing or to solve language conflict situations in bilinguals (caudate nucleus, posterior cingulate gyrus, STG, precuneus). Further, the activation of these areas was found to be higher in 2L1 compared to L2L. Conclusion: The coupling of longer reaction times to the recruitment of extra language-related brain areas supports the hypothesis that when dealing with language conflicts the specialization of bilinguals hampers the way they can process with nonverbal conflicts, at least at early stages in life

Professionals’ views on the use of smartphone technology to support children and adolescents with memory impairment due to acquired brain injury

Purpose: To identify from a health-care professionals’ perspective whether smartphones are used by children and adolescents with acquired brain injury as memory aids; what factors predict smartphone use and what barriers prevent the use of smartphones as memory aids by children and adolescents. Method: A cross-sectional online survey was undertaken with 88 health-care professionals working with children and adolescents with brain injury. Results: Children and adolescents with brain injury were reported to use smartphones as memory aids by 75% of professionals. However, only 42% of professionals helped their clients to use smartphones. The only factor that significantly predicted reported smartphone use was the professionals’ positive attitudes toward assistive technology. Several barriers to using smartphones as memory aids were identified, including the poor accessibility of devices and cost of devices. Conclusion: Many children and adolescents with brain injury are already using smartphones as memory aids but this is often not facilitated by professionals. Improving the attitudes of professionals toward using smartphones as assistive technology could help to increase smartphone use in rehabilitation

Self, memory, and imagining the future in a case of psychogenic amnesia

We report a case of psychogenic amnesia and examine the relationships between autobiographical memory impairment, the self, and ability to imagine the future. Case study JH, a 60 year old male, experienced a 6 year period of pervasive psychogenic amnesia covering all life events from childhood to the age of 53. JH was tested during his amnesic period and again following hypnotherapy and the recovery of his memories. JH’s amnesia corresponded with deficits in self-knowledge and imagining the future. Results are discussed with reference to models of self and memory and processes involving remembering and imagining

The role of the dominant versus the non-dominant hemisphere: an fMRI study of Aphasia recovery following stroke

Background: Speech production is one of the most frequently affected cognitive functions following stroke; however, the neural mechanisms underlying the recovery of speech function are still incompletely understood. Aims: The current study aims to address the differential contributions of the dominant and non-dominant hemispheres in recovery from aphasia following stroke by comparing data from four stroke patients and 12 control participants to assess the patterns of activation during speech production tasks during functional magnetic resonance imaging (fMRI) scanning. Methods & Procedures: Four chronic stroke patients (three left-hemisphere lesion and one right-hemisphere lesion) diagnosed with Broca’s aphasia at the acute phase, but now recovered to near normal speech ability, were tested on speech production tasks (phonemic fluency, categorical fluency and picture naming) whilst undergoing fMRI. These patients were compared with 12 healthy controls undergoing the same procedure. Outcomes & Results: Individual subject analysis showed activation peaks in perilesional areas in three out of four patients. This included one patient with right-hemisphere lesion, who also showed predominant perilesional activation. Group analysis of control participants showed predominately left-hemisphere activation, but not exclusively so. Laterality indexes were calculated and showed predominant left-hemisphere lateralisation in the control group (LI = 0.4). Three out of the four patients showed speech lateralised to the same hemisphere as their lesion and the fourth patient showed speech lateralised to the opposite hemisphere to their lesion. Different speech production tasks resulted in varying lateralisation indices (LIs) within participants. Conclusions: The data suggest that perilesional areas support recovery of speech in the chronic phase post-stroke regardless of the site of the lesion. The study has implications for the understanding of functional recovery as well as for the paradigms used in fMRI to localise speech production areas. Specifically, a variety of speech tasks are required to elicit activation that is representative of the range of cortical involvement in speech in healthy adults and that also allows for accurate reporting of the extent of recovery experienced in patients

Cognitive tests used in chronic adult human randomised controlled trial micronutrient and phytochemical intervention studies

In recent years there has been a rapid growth of interest in exploring the relationship between nutritional therapies and the maintenance of cognitive function in adulthood. Emerging evidence reveals an increasingly complex picture with respect to the benefits of various food constituents on learning, memory and psychomotor function in adults. However, to date, there has been little consensus in human studies on the range of cognitive domains to be tested or the particular tests to be employed. To illustrate the potential difficulties that this poses, we conducted a systematic review of existing human adult randomised controlled trial (RCT) studies that have investigated the effects of 24 d to 36 months of supplementation with flavonoids and micronutrients on cognitive performance. There were thirty-nine studies employing a total of 121 different cognitive tasks that met the criteria for inclusion. Results showed that less than half of these studies reported positive effects of treatment, with some important cognitive domains either under-represented or not explored at all. Although there was some evidence of sensitivity to nutritional supplementation in a number of domains (for example, executive function, spatial working memory), interpretation is currently difficult given the prevailing 'scattergun approach' for selecting cognitive tests. Specifically, the practice means that it is often difficult to distinguish between a boundary condition for a particular nutrient and a lack of task sensitivity. We argue that for significant future progress to be made, researchers need to pay much closer attention to existing human RCT and animal data, as well as to more basic issues surrounding task sensitivity, statistical power and type I error

Priming letters by colors: evidence for the bidirectionality of grapheme–color synesthesia

In synesthesia, stimulation of one sensory modality leads to a percept in another nonstimulated modality, for example, graphemes trigger an additional color percept in grapheme–color synesthesia, which encompasses the variants letter–color and digit–color synesthesia. Until recently, it was assumed that synesthesia occurs strictly unidirectional: Although the perception of a letter induces a color percept in letter–color synesthetes, they typically do not report that colors trigger the percept of a letter. Recent data on number processing in synesthesia suggest, however, that colors can implicitly elicit numerical representations in digit–color synesthetes, thereby questioning unidirectional models of synesthesia. Using a word fragment completion paradigm in 10 letter–color synesthetes, we show here for the first time that colors can implicitly influence lexical search. Our data provide strong support for a bidirectional nature of grapheme–color synesthesia and, in general, may allude to the mechanisms of cross-modality interactions in the human brain