Neuronal functional diversity and collective behaviors

Abstract

A major question in today's neuroscience is how the brain's complex operations and organization emerge from individual components. The robustness of neuronal properties with flexible linkages between regulatory processes conceivably accounts for the adaptive, tunable, multistable dynamics; the coding schemes; and the complexity of neuronal functional (sub)systems. Interneurons and neurotransmitter diversity, resonance phenomena due to properties of the cell, time/frequency-dependent activation of dedicated neuronal assemblies, and code- and frequency-specific oscillations interact in determining the brain functional setup and operations. Such an arrangement would also provide the functional requirements for access to neural mechanisms, dedicated neuronal circuitry and the proper timing allowing for the selective differentiation among cortical neurons due to performing in different tasks. No comprehensive theory or systematic methodological approach appears yet conceivable. The scenario, however incomplete and incompletely characterized, is nevertheless promising and warrants further investigation.

Fig. 1

Superimposed visual responses to appearing (onset) and reversing 5-ms bursts of dynamical white noise at different intensities recorded from a healthy subject; in inset, specimens of the responses to noise onset from a second subject (the noise intensities were set and are indicated as in [74]). Note the response occurring when the burst of white noise was presented, with no detectable response when it was reversed, and the intensity/amplitude function. Stimulation and recording paradigms were consistent with the international guidelines to record the human cortical visual responses to contrast stimulation for diagnostic or research purposes [109]. However, the white noise estimated spatial frequency (~45 cycle/degrees) was incompatible with the human contrast sensitivity function and stimulus reversal yielded no response, whereas contrast activation would. Stimulation was monocular (right eye). Noise static images were obtained by adding to each pixel a random number uniformly chosen over a discrete interval; dynamic noise was obtained by presenting several static images in a rapid sequence over the 5-ms stimulus duration. The stimulus was reversed by turning black pixels into white and white into black, with the overall luminance remaining constant. Electrodes (dermal Ag/AgCl) were conventionally positioned 5 cm laterally to the inion and 5% of the inion-to-nasion distance above the inion, with reference electrode at Fpz and ground at Cz. Preliminary, unpublished data obtained in collaboration with Dr. S. Carozzo (Dept. of Motor Science) and prof. M. Riani’s group (Dept. of Physics) from the University of Genova, Italy