Contributions published at Banking (Stefano Battiston)

The boards of large corporations sharing some of their directors are connected in complex networks. Boards are responsible for corporations' long-term strategy and are often involved in decisions about a common topic related to the belief in economical growth or recession. We are interested in understanding under which conditions a large majority of boards making the same decision can emerge in the network. We present a model where board directors are engaged in a decision-making dynamics based on "herd behavior." Boards influence each other through shared directors. We find that imitation of colleagues and opinion bias due to the interlock do not trigger an avalanche of identical decisions over the board network, whereas the information about interlocked boards' decisions does. There is no need to invoke global public information, nor external driving forces. This model provides a simple endogenous mechanism to explain the fact that boards of the largest corporations of a country can, in the span of a few months, make the same decisions about general topics.

Rats explore their surroundings through rhythmic movement of their mystacial vibrissae. At any given moment, multiple whiskers are simultaneously moved and may contact the surface of an object. The aim of this work is to understand how simultaneous multiple-whisker deflections are processed in the somatosensory cortex. Arrays of 25 electrodes were inserted into the vibrissal representation of barrel cortex of adult rats. Multi-unit responses were recorded during (i) stimulation of single whiskers, and (ii) simultaneous stimulation of two, three or four whiskers of a whisker arc or whisker row. The whole-array response elicited by the simultaneous stimulation of multiple-whiskers (observed response) was compared to a multiple-whisker response predictor, defined as the sum of the whole-array responses to the separate stimulation of the corresponding single whiskers. The observed response to stimulation of four whiskers was nearly always less than the predicted response, indicating a sublinear summation of multiple coincident inputs. Examining the poststimulus time course of sublinearity, we found that the earliest cortical response to whisker deflection – reflecting the thalamocortical volley - was linear, whereas the successive cortical response was highly sublinear. This suggests a cortical origin of the phenomenon.

In this report, the input/output relations in an isolated ganglion of the leech Hirudo medicinalis were studied by simultaneously using six or eight suction pipettes and two intracellular electrodes. Sensory input was mimicked by eliciting action potentials in mechanosensory neurons with intracellular electrodes. The integrated neural output was measured by recording extracellular voltage signals with pipettes sucking the roots and the connectives. A single evoked action potential activated electrical activity in at least a dozen different neurons, some of which were identified. This electrical activity was characterized by a high degree of temporal and spatial variability. The action potentials of coactivated neurons, i.e. activated by the same mechanosensory neuron, did not show any significant pairwise correlation. Indeed, the analysis of evoked action potentials indicates clear statistical independence among coactivated neurons, presumably originating from the independence of synaptic transmission at distinct synapses. This statistical independence may be used to increase reliability when neuronal activity is averaged or pooled. It is suggested that statistical independence among coactivated neurons may be a usual property of distributed processing of neuronal networks and a basic feature of neural computation.