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The evidence reviewed in the paper shows that the spreading depression (SD) belongs to the mass of closely packed neurons which can support qualitatively new phenomena occurring at a more primitive level of cellular interaction. The latter becomes prepotent under extreme conditions, overloading the local energy supply and homeostatic mechanisms. The two levels of neural integration, the highly heterogeneous specifically connected synaptic level and the statistically uniform diffusively organized nonsynaptic level, are always present in all forms of brain activity and mutually influence each other. While phenomena mediated by nonsynaptic interaction overrule the synaptic ones under resting conditions, excessive synaptic excitation may either switch the affected brain region from synaptic to nonsynaptic interaction (spike-triggered SD) or assert the synaptic interaction over the nonsynaptic one (functional blockade of SD). Nonsynaptic interaction is an inherent property of brain, an obligatory consequence of the trade-off between maximal packing density and independent function of individual elements of the system which sets definite limits to the maximum activation of synaptic processes, contributes to slow synchronization of neural populations and plays an important role in various instances of brain pathology. The phenomena generated at this level belong to the family of autowaves, share their typical properties and can be described by similar formal rules.

Using both techniques of thermovision and statistical analysis of thermal imaging, dynamics of temperature distribution over the dorsal surface of the brain were investigated through the intact skull during acute experiments on white rats. Both diffuse and regionally specific cerebral thermal reactions were observed during visual, acoustic, and somatosensory stimulation, together with multiple local thermal response, often following a specific pattern. These outline thermal effects differing from the compartment of the brain to another in degree, stability, and point of onset. Temperature waves developed together with spreading depression, produced in the cortex by injecting KC1. Once investigations had been performed this response could be divided into diffuse and spatially ordered components. The possible mechanisms of this thermal imaging of brain processes are discussed, together with how they are linked with changes in cerebral blood flow and neuronal metabolic thermal production.