Dynamics of evoked potentials in cortical projection structures during a retarded instrumental defense reflex in dogs]

Evoked potentials (EP) in the somatosensory and auditory cortical areas were studied in four dogs against the background of a retarded defensive instrumental conditioned reflex to clicks. Four phases of the reflex were singled out by the changes in the structure of EP late components (LC) in the two projection zones. The most complex LC changes in the form of intensified negative components and the appearance of additional negative LC are recorded in response to the first click of the series and to the one followed by the conditioned motor reaction (CMR). Against the background of CMR delay, the EPs increased, while during the CMR, they decreased, owing to the diminished negative components, while the positive components were preserved and sometimes intensified. An assumption has been made that cortical projection structures of paired stimuli function in one and the same regime.     

Vestibular nuclei of hemilabyrinthectomized guinea pigs during decompensation.

1. The effects of the post-brachial section of the spinal cord on the field potentials recorded from the vestibular nuclei during stimulation of the right vestibular receptors have been studied in left hemilabyrinthectomized and then compensated guinea pigs. 2. Facilitation of the field potentials in the right vestibular nuclear complex and inhibition in the left nuclei have been observed. 3. These results confirm that the spinal cord is involved in the compensation of the release syndrome brought about by the lesion of one labyrinth. 4. The possible mechanisms underlying such a compensation are discussed.     

Evoked activity in the ventral horn of the lumbar segments of the spinal cord during cortical inhibition of cortical motor responses

Electrical activity in the flexor nerve and focal potentials (FP) in the medial and lateral zones of the ventral horn (VH) of segments L₆ and L₇ of the spinal cord, evoked by excitation of the contralateral motor cortex, were recorded in delicate experiments on cats. These focal potentials were studied during inhibition of the flexor response that developed as a result of prior excitation of the ipsilateral cortex ("cortical inhibition"). During the inhibition the FP's of the medial zone (layer VIII, according to Rexed) were greatly increased, mainly in their negative components, their time-characteristics being altered. When the interval between excitations was 50 msec (in that case the inhibition was most pronounced) the medial FP's arose against a negative background, which was a late component of the previous activity evoked by conditioning excitation. The appearance of this late component was correlated with the development of inhibition of the cortical flexor response. At the same time a positive condition developed in the lateral zone, in the region of the nucleus biceps-semitendinosus, which indicated orientation in a lateral direction of the interneurons discharging in the medial zone at late periods after the conditioning excitation. Inhibition of the flexor response was accompanied by depression of the lateral FP's without change in their sign or in the time-structure of their components. It is suggested that cortical inhibition of the cortical flexor response arises at the interneuron level. The functional structure of that inhibitory pathway is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 185–193, March–April, 1971.     

Sonic hedgehog expression in corticofugal projection neurons directs cortical microcircuit formation

The precise connectivity of inputs and outputs is critical for cerebral cortex function; however, the cellular mechanisms that establish these connections are poorly understood. Here, we show that the secreted molecule Sonic Hedgehog (Shh) is involved in synapse formation of a specific cortical circuit. Shh is expressed in layer V corticofugal projection neurons and the Shh receptor, Brother of CDO (Boc), is expressed in local and callosal projection neurons of layer II/III that synapse onto the subcortical projection neurons. Layer V neurons of mice lacking functional Shh exhibit decreased synapses. Conversely, the loss of functional Boc leads to a reduction in the strength of synaptic connections onto layer Vb, but not layer II/III, pyramidal neurons. These results demonstrate that Shh is expressed in postsynaptic target cells while Boc is expressed in a complementary population of presynaptic input neurons, and they function to guide the formation of cortical microcircuitry. VIDEO ABSTRACT:     

The role of vestibular afferent input in systemic interactions of cortical areas in the human brain

To investigate the role of vestibular afferent input in systemic interactions between cortical areas of the human brain, the dynamics of interregional cortical interactions has been studied in patients with cervical dystonia during their therapy by the removal of the transtympanic chemical vestibular receptor. It has been found that even unilateral vestibular dereception leads to a profound reorganization of systemic interactions between remote cortical areas, particularly, the anterior and posterior associative areas in both hemispheres. Relationships indicating the role of vestibular input in the organization of integrative brain activity have been found, which confirms its systemic role.