No abstract

Environmental enrichment (EE) is an experimental protocol based on a complex sensorimotor stimulation that dramatically affects brain development. While it is widely believed that the effects of EE result from the unique combination of different sensory and motor stimuli, it is not known whether and how cortico-cortical interactions are shaped by EE. Since the primary visual cortex (V1) is one of the best characterized targets of EE, we looked for direct cortico-cortical projections impinging on V1, and we identified a direct monosynaptic connection between motor cortex and V1 in the mouse brain. To measure the interactions between these areas under standard and EE rearing conditions, we used simultaneous recordings of local field potentials (LFPs) in awake, freely moving animals. LFP signals were analyzed by using different methods of linear and nonlinear analysis of time series (cross-correlation, mutual information, phase synchronization). We found that EE decreases the level of coupling between the electrical activities of the two cortical regions with respect to the control group. From a functional point of view, our results indicate, for the first time, that an enhanced sensorimotor experience impacts on the brain by affecting the functional crosstalk between different cortical areas.

We analyze RR heartbeat sequences with a dynamic model that satisfactorily reproduces both the long-and the short-time statistical properties of heart beating. These properties are expressed quantitatively by means of two significant parameters, the scaling ␦ concerning the asymptotic effects of long-range correlation, and the quantity 1Ϫ establishing the amount of uncorrelated fluctuations. We find a correlation between the position in the phase space (␦,) of patients with congestive heart failure and their mortality risk. The main purpose of this Brief Report is twofold. The first goal is to afford a firmer theoretical basis to the method of analysis of heartbeating proposed in an earlier publication ͓1͔. The second goal is to substantiate with more convincing arguments that this method yields an efficient criterion to estimate the mortality risk of congestive heart failure ͑CHF͒ patients.To prove this significant diagnostic property, we illustrate the relevant clinical data, missing in the earlier publication, and we limit ourselves to affording only this kind of ''experimental'' information. For other details, already adequately illustrated in the earlier publication, we refer the interested reader to Ref. ͓1͔. For this study we considered 13 male CHF patients, from a study base of 320 subjects, who experienced cardiac death during a follow-up of 26 months ͑average 19 months, median 22 months͒. Inclusion criteria were absence of pulmonary or neurological disease, absence of acute myocardial infarction or cardiac surgery within the previous six months, absence of any other disease limiting survival, stable therapy for at least two weeks, and good quality 24-h Holter recordings, with an ectopy rate less than 5%. A comparable number of control subjects ͑16 patients͒, matching for age, sex, NYHA class ͑a functional and therapeutic classification for prescription of physical activity for cardiac patients͒, and etiology, was then selected. These latter patients did not experience cardiac death after follow-up. All patients had a 24-h Holter recording at baseline, together with standard functional evaluation including measurement of left ventricular ejection fraction, peak VO2 (O 2 consumption during effort͒, and sodium ͑Na͒. Finally, RR series for 10 healthy subjects were taken from the Nonlinear Time Series Analysis ͑NOLTISALIS͒ archive ͓2͔.

By using a single compartment biophysical model of a fast spiking interneuron the synchronization properties of a pair of cells, coupled by electrical and inhibitory synapses, are investigated. The inhibitory and excitatory synaptic couplings are modeled in order to reproduce the experimental time course of the corresponding currents. It is shown that increasing the conductance value of the electrical synapses enhances the synchronization between the spike trains of the two cells. Moreover, increasing either the decay time constant of the inhibitory current or the firing frequency of the cells favours the emergence of synchronous discharges.