Information transmission and criticality in the contact process

Marzio Cassandro, Antonio Galves and Eva Löcherbach

In the present paper, we study the relation between criticality and information transmission in the one-dimensional contact process with infection parameter λ. To do this we define the {\it sensitivity} of the process to its initial condition. This sensitivity increases for values of λ ‹ λc, the value of the critical parameter. The main point of the present paper is that we show that actually it continues increasing even after λc and only starts decreasing for sufficiently large values of λ. This provides a counterexample to the common belief that associates maximal information transmission to criticality.

An overview of mathematical literacy in Brazil: an interview with PISA analyst Esther Carvalhaes

"Most students in Brazil, after spending many years in compulsory education, are unable to make use of mathematics concepts and procedures to perform even basic operations and solve very simple problems.” This statement comes from the OECD's PISA analyst Esther Carvalhaes, who came to Brazil as a NeuroMat guest for a series of events on mathematical literacy. She was interviewed by the NeuroMat dissemination team in the occasion.

Video: Soccer derby in the brain

Time-lapsed visual representation of the vulgarization article "Fla-flu no cérebro," by Antonio Galves. Production: Giulia Ebohon.

Effect of synaptic plasticity on functional connectivity and global activity of a neocortical network model

Renan O. Shimoura, Rodrigo F.O. Pena and Antonio C. Roque

Neocortex plays key role in diverse brain functions. Understanding this role involves the study of collective neural activity patterns under different situations, and how these patterns relate to the structural and functional organization of neocortex. Here we study the effect of synaptic plasticity on neural spiking activity patterns in a neocortical network model. We measure changes in neural spiking patterns due to changes in the strengths of the synapses connecting neurons and relate them to changes in the functional connectivity of the network as disclosed by graph-theoretic measures.

Our neocortical network model was composed of excitatory and inhibitory neurons in the proportion of four excitatory cells for each inhibitory cell. Neurons were described by the Izhikevich model [1]. The parameters of the model were adjusted so that excitatory neurons were of the regular spiking (RS) type and inhibitory neurons were all of either the fast spiking (FS) or the low-threshold spiking (LTS) type. Synapses were modeled as event-based, and two types of synaptic dynamics were considered: one without synaptic plasticity in which the synaptic weight received a fixed increment after the pre-synaptic event and decayed exponentially after that, and one with synaptic plasticity in which the synapse obeyed an asymmetric spike-timing dependent plasticity (STDP) rule described by [2]. Neurons were organized into four layers (2/3, 4, 5 and 6) with layer- and cell-specific statistical connectivity rules based on [3]. The total number of neurons in the model was about 4,000. Two experiments were done: one with all synapses described by the model without synaptic plasticity, and the other with synapses between excitatory neurons described by the STDP rule while the remaining synapses were described by the model without synaptic plasticity. In both cases, the model was stimulated by a current injection of random amplitude applied to neurons of layer 4 (L4), which is the main input layer of the cortex. The spiking activity of the network was evaluated by measures extracted from the raster plot of the spikes produced by the neurons, e.g. layer-specific and network mean and time-dependent firing rates. The structural and functional connectivities of the network were represented by the respective structural and functional adjacency matrices. The functional adjacency matrix was constructed by taking in consideration neuron pairs with strength of their synaptic coupling above a specific threshold. The topology of the adjacency matrices was characterized by graph-theoretic measures, e.g. clustering coefficient.

We determined a set of parameters for which the spiking activity generated in L4 by the external input propagated to the entire network. This network-wide activity was oscillatory, and we found that its mean frequency was higher for the network version with synaptic plasticity than for the version without synaptic plasticity. We also found that the formation of clusters of synchronous neural activity was facilitated in the case with LTS cells as inhibitory neurons. Our results suggest that synaptic plasticity may induce changes in the functional connectivity of the neocortical network with impact on its global activity.

A Naturalistic Assessment of the Organization of Children’s Memories Predicts Cognitive Functioning and Reading Ability

Natália Bezerra Mota, Janaína Weissheimer, Beatriz Madruga, Nery Adamy, Silvia A. Bunge, Mauro Copelli and Sidarta Ribeiro

To explore the relationship between memory and early school performance, we used graph theory to investigate memory reports from 76 children aged 6–8 years. The reports comprised autobiographical memories of events days to years past, and memories of novel images reported immediately after encoding. We also measured intelligence quotient (IQ) and theory of mind (ToM). Reading and Mathematics were assessed before classes began (December 2013), around the time of report collection (June 2014), and at the end of the academic year (December 2014). IQ and ToM correlated positively with word diversity and word-to-word connectivity, and negatively with word recurrence. Connectivity correlated positively with Reading in June 2014 as well as December 2014, even after adjusting for IQ and ToM. To our knowledge, this is the first study demonstrating a link between the structure of children's memories and their cognitive or academic performance.




The Research, Innovation and Dissemination Center for Neuromathematics is hosted by the University of São Paulo and funded by FAPESP (São Paulo Research Foundation).


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