Cerebral cortex: the singular precision of visual cortex maps

A remarkable new technique, two-photon confocal fluorescence microscopy, has revealed an extraordinarily precise organization in the visual cortex. The methodology seems set to become the tool of choice for studying cortical maps.     

Hypertrophy of the adrenal cortex

The human adrenal cortex in essential hypertension and in the salt-losing form of the adrenogenital syndrome and the adrenal cortex in spontaneously hypertensive rats were studied by morphometry. Under long-term functional loading hypertrophy of adrenocortical cells is the common way of increasing the mass of the cortex. The correlation between the morphological parameters of the adrenocortical structures increases in this condition. Hyperplasia along with hypertrophy has been found in man at an early age. The differences in the degree of hypertrophy of the nuclei and nucleoli may be connected with different intensity of adrenocortical function in different pathological conditions.     

Cholecystokinin from the entorhinal cortex enables neural plasticity in the auditory cortex

Patients with damage to the medial temporal lobe show deficits in forming new declarative memories but can still recall older memories, suggesting that the medial temporal lobe is necessary for encoding memories in the neocortex. Here, we found that cortical projection neurons in the perirhinal and entorhinal cortices were mostly immunopositive for cholecystokinin (CCK). Local infusion of CCK in the auditory cortex of anesthetized rats induced plastic changes that enabled cortical neurons to potentiate their responses or to start responding to an auditory stimulus that was paired with a tone that robustly triggered action potentials. CCK infusion also enabled auditory neurons to start responding to a light stimulus that was paired with a noise burst. In vivo intracellular recordings in the auditory cortex showed that synaptic strength was potentiated after two pairings of presynaptic and postsynaptic activity in the presence of CCK. Infusion of a CCK_B antagonist in the auditory cortex prevented the formation of a visuo-auditory association in awake rats. Finally, activation of the entorhinal cortex potentiated neuronal responses in the auditory cortex, which was suppressed by infusion of a CCK_B antagonist. Together, these findings suggest that the medial temporal lobe influences neocortical plasticity via CCK-positive cortical projection neurons in the entorhinal cortex.     

Neuronal specialization of the motor cortex in normal rabbits and following destruction of the visual cortex

The activity of neurones of the anterolateral part of the motor cortex in food-acquisition behaviour was compared in two control rabbits and in three rabbits after the operation of bilateral ablation of the striatal cortex. In two of three operated rabbits the pattern of behavioural specialization lost considerably the specificity peculiar to the motor cortex (predominance of G-neurones activated in grasping of food), approaching (but not becoming identical) the pattern of specialization of the visual cortex neurones: the number of G-neurones decreased in a half, and the number of L-neurones (activated in connection with the acts of instrumental food-acquisition behaviour which animals were trained to in the experimental cage) was doubled. Changes of the activity were significantly less expressed in the third operated rabbit. The number of the neurones activated in food-acquisition behaviour in operated rabbits in comparison with the control ones was reduced in the upper layers of the cortex and increased in the lower layers. The resemblance is discussed of the basic processes of animals learning and behaviour recovery.     

Innervation of the renal cortex.

Morphologic studies of renal innervation have utilized the methods of histochemistry and electron microscopy. Much information has been derived from examination of the renal cortex in monkey and rat. Fluorescence histochemistry shows a rich adrenergic innervation. Acetylcholinesterase can be demonstrated histochemically in the renal nerves by light and electron microscopy. Studies in the rat using 6-hydroxydopamine, a drug that selectively destroys adrenergic nerves, indicate that the glomerular arterioles and surrounding tubules are innervated by adrenergic nerves containing acetylcholinesterase. Distinct neurovascular and neurotubular junctions are observed the electron microscope. They are anatomically consistent with being the sites of synaptic transmission. Ultrastructural analysis of serial sections reveals that single individual axons contact multiple vascular cells and renal tubules. We now have a considerable body of information concerning the morphology of renal innervation are are beginning to appreciate the role of the renal nerves in kidney function.     

The chronoarchitecture of the cerebral cortex

We review here a new approach to mapping the human cerebral cortex into distinct subdivisions. Unlike cytoarchitecture or traditional functional imaging, it does not rely on specific anatomical markers or functional hypotheses. Instead, we propose that the unique activity time course (ATC) of each cortical subdivision, elicited during natural conditions, acts as a temporal fingerprint that can be used to segregate cortical subdivisions, map their spatial extent, and reveal their functional and potentially anatomical connectivity. We argue that since the modular organisation of the brain and its connectivity evolved and developed in natural conditions, these are optimal for revealing its organisation. We review the concepts, methodology and first results of this approach, relying on data obtained with functional magnetic resonance imaging (fMRI) when volunteers viewed traditional stimuli or a James Bond movie. Independent component analysis (ICA) was used to identify voxels belonging to distinct functional subdivisions, based on their differential spatio-temporal fingerprints. Many more regions could be segregated during natural viewing, demonstrating that the complexity of natural stimuli leads to more differential responses in more functional modules. We demonstrate that, in a single experiment, a multitude of distinct regions can be identified across the whole brain, even within the visual cortex, including areas V1, V4 and V5. This differentiation is based entirely on the differential ATCs of different areas during natural viewing. Distinct areas can therefore be identified without any a priori hypothesis about their function or spatial location. The areas we identified corresponded anatomically across subjects, and their ATCs showed highly area-specific inter-subject correlations. Furthermore, natural conditions led to a significant de-correlation of interregional ATCs compared to rest, indicating an increase in regional specificity during natural conditions. In contrast, the correlation between ATCs of distant regions of known substantial anatomical connections increased and reflected their known anatomical connectivity pattern. We demonstrate this using the example of the language network involving Broca's and Wernicke's area and homologous areas in the two hemispheres. In conclusion, this new approach to brain mapping may not only serve to identify novel functional subdivisions, but to reveal their connectivity as well.     

Morphology of the cat auditory cortex

The ultrastructural features of the primary auditory cortex of the cats and the character of the endings of geniculo-cortical afferent fibers in the early stages of experimental degeneration evoked by destruction of the medial geniculate body were studied. In all layers of the cortex asymmetrical synapses with round synaptic vesicles on dendritic spines and on thin dendritic branches of pyramidal and nonpyramidal neurons are predominant. Symmetrical synapses with flattened or polymorphic vesicles are distributed chiefly on the bodies of the neurons and their large dendrites. Because there are few symmetrical synapses which could be regarded as inhibitory it is postulated that inhibitory influences may also be transmitted through asymmetrical synapses with round vesicles. Other types of contacts between the bodies of neurons, dendrites, and glial processes also were found in the auditory cortex. Degenerating terminals of geniculo-cortical fibers were shown to terminate chiefly in layer IV of the cortex on pyramidal and nonpyramidal neurons. Degeneration was of the dark type in asymmetrical synapses with round vesicles. The results are dicussed in connection with electrophysiological investigations of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 519–524, September–October, 1973.