Evaluation of hippocampal infolding using magnetic resonance imaging.

To investigate developmental morphological variation of the hippocampal formation, we evaluated the degree of hippocampal infolding in cross-sectional oblique coronal images of the cerebral peduncle and the superior cerebellar peduncle. We defined the hippocampal infolding angle as the angle between the vertical midline and the straight line connecting the medial superior margin of the subiculum with the lateral margin of the cornu ammonis. The angle increased slightly with age, and was larger in the superior cerebellar peduncle than in the cerebral peduncle and larger in the right superior cerebellar peduncle than in the left superior cerebellar peduncle. This suggests that this angle and its variation with age and location merit our attention in morphological evaluation of the hippocampal formation.

Apoptosis of auditory neurons following central process injury.

Although apoptotic changes in auditory neurons induced by injury to peripheral processes (dendrites) have been intensively studied, apoptotic changes in auditory neurons induced by injury to central processes (axons of spiral ganglion cells, SGCs) have not been reported previously, probably due to lack of an experimental model. The present study reports for the first time the appearance, extent, and time course of SGC apoptosis following injury to the central processes. Apoptosis was studied in a rat model that consisted of compression of the auditory nerve in the cerebellopontine (CP) angle cistern with intraoperative recordings of auditory nerve compound action potentials (CAPs) to ensure highly reproducible results. Rats were killed between day 0 and day 14 after compression and apoptosis of SGCs was evaluated quantitatively as well as qualitatively by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining, anti-activated caspase-3 immunostaining, Hoechst 33342 staining, and electron microscopy. The average number of TUNEL-positive apoptotic SGCs in each cochlear turn increased from day 1 to day 5 and then decreased gradually to an undetectable level on day 14 after compression. The average proportion of apoptotic SGCs identified in any cochlear turn on any day was always lower than 10%. The results of our present study should be useful in determining the therapeutic time window for rescuing auditory neurons undergoing apoptosis due to injury during surgery in the CP angle.

Salient anatomic features of the cortico-ponto-cerebellar pathway.

Recent studies of the primate corticopontine projection show that the neocerebellum--in addition to connections from motor and sensory areas--receives connections from various association areas of the cerebral cortex, some of which are thought to be primarily engaged in cognitive tasks. The quantities of such connections in relation to those from more clearly motor-related parts of the cortex need to be more precisely determined, however. Furthermore, the anatomic data on origin of corticopontine fibers needs to be supplemented with physiological experiments to clarify their functional properties at the single-cell level. For example, nothing is known of the functional role of the large input from the cingulate gyrus, nor is the input from the posterior parietal cortex physiologically characterized. Finally, the scarcity of corticopontine connections from the prefrontal cortex in the monkey (and probably also in man) may not seem readily compatible with a prominent role of the neocerebellum in certain cognitive tasks. We discuss data--in particular from three-dimensional reconstructions--indicating that both corticopontine projects and pontocerebellar neurons are arranged in a lamellar pattern. Corticopontine and pontocerebellar lamellae have similar shapes and orientations but appear to differ in other respects. Corticopontine terminal fields are sharply delimited, apparently without gradual overlap between projections from different sites in the cortex, whereas pontocerebellar lamellae are more fuzzy and exhibit gradual overlap of neuronal populations projecting to different targets. In spite of the sharpness of the corticopontine projection, there may be many opportunities for convergence of inputs from different parts of the cortex. Thus, the wide divergence of corticopontine projections produces many sites of overlap, and extensive interfaces between different terminal fields enabling convergence of inputs onto each neuron. We suggest that the lamellar arrangement of corticopontine terminal fields and of pontocerebellar neurons serve to create diversity of pontocerebellar neuronal properties. Thus, each small part of the cerebellar cortex would receive a specific combination of messages from many different sites in the cerebral cortex. The spatial arrangement of cerebrocerebellar connections have to be understood both in terms of fairly simple large-scale, gradual topographic relationships and an apparently highly complex pattern of divergence and convergence. Developmental studies of corticopontine and of pontocerebellar projections together with three-dimensional reconstructions in adults suggest that the highly complex adult connectional pattern may be created by simple rules operating during development.

[The dream as mind's "organizer": neuropsychological contribution into the function and significance of the oneiric activity]. / Il sogno come "regista" della mente: contributo neuropsicologico sulla funzione e sul significato dell'attività onirica.

The author examines the oneiric activity in a neuropsychologic prospect, as he considers this approach as valid and capable of giving good results for the understanding of psychic phenomena. After explaining synthetically the principles of the psychophysiologic school of Chicago, of the neuro-physiologic school of professor M. Jouvet in Lyon, and the theoretic hypotheses derived from clinical knowledge like that of the neurologist O. Sacks, the author develops Jouvet's principle of the dream as "endogenous phylogenetic learning". The author is of the opinion that the dream, from a psycho-biological standpoint, has such features that it can be considered as a process that is very similar to the creative one, as intended by S. Arieti, and that has its roots in the "homo naturalis". The oneiric activity seems to be able to implement a creative synthesis between nature and culture, between soma and psyche, between rational world and archetypalinstinctive world, in compliance with the fundamental creative process on which the evolution is based, as explained by K. Lorenz and Teilhard de Chardin with the expressions "unity from diversity" and "créer c'est unir". Therefore, it can be an instrument capable of helping the contemporary man, whose identity is threatened by the excessive discrepancy between the rational conscious process, that is conditioned by the extremely quick cultural transformation (mainly due to technology) and the unconscious archetypal-instinctive process, which is connected with the slow phylogenetic evolution.

[Electrophysiological identification of the cochlear and vestibular nerves in the cerebellopontine angle: experimental study and clinical implication].

Electrical stimulation was applied on the surface of the eighth cranial nerve in the cerebellopontine angle of dogs and the evoked potentials were recorded with surface electrodes on the scalp. The shape of the evoked potentials recorded was different according to the portion of the nerve stimulated electrically. It was, therefore, possible to precisely identify the nerve stimulated from the surface recorded evoked potentials. This electrophysiological method may be helpful for the surgeon to precisely locate the cochlear and vestibular nerves in various operations in the cerebellopontine angle in human. Our preliminary experience of this monitoring method in acoustic neuroma excision was presented.

A comparison of magnetic and electrical stimulation of facial nerve at the cerebello-pontine angle in the dog.

Magnetic stimulation is a painless, non-invasive technique which allows an alternative method for testing cranial nerves which were previously inaccessible. We compared the latency of muscle responses obtained by electrical stimulation of the facial nerve at the cerebello-pontine angle (CPA) to high intensity transcranial magnetic stimulation (TMS) in 6 dogs. Evoked muscle response from the levator nasolabialis during electrical stimulation had a mean latency of 6.24 +/- 0.42 msec, compared with a mean of latency of 6.13 +/- 0.50 msec obtained by magnetic stimulation. Orbicularis oculi had a mean latency of 3.65 +/- 0.34 msec compared with a mean latency of 3.53 +/- 0.36 msec for magnetic stimulation. This suggests that high intensity TMS results in direct activation of the facial nerve as it exits the brain-stem in dogs. This observation is in accord with previous clinical studies that magnetic stimulation results in activation of the intracranial segment of the facial nerve in man.

Deterioration of auditory evoked potentials during cerebellopontine angle manipulations. An interpretation based on an experimental model in dogs.

Evoked action potentials from the internal auditory meatus portion of the cochlear nerve (IAM-EAP's) and brain-stem auditory evoked potentials (BAEP's) from the vertex were simultaneously recorded during cerebellopontine angle (CPA) manipulations (retractions of the cerebellar hemisphere and the cochlear nerve) in dogs. The BAEP changes noted in these dogs were the same as those seen in patients. The IAM-EAP's showed graded deterioration related to BAEP changes. The results are as follows: Prolongation of the I-V interpeak latency of BAEP's, the most common finding during CPA manipulations, is the reflection of prolongation of the I-II interpeak latency, which is caused by conduction impairment or block of the nerve impulses between the extracranial portion of the cochlear nerve and the brain stem. The operative manipulations representing stretch or compression injury to the cochlear nerve in the CPA leads to an acute traumatic cranial nerve root lesion--a retrocochlear lesion. The obliteration of all BAEP components including wave I cannot be caused by conduction block. This is caused by occlusion of the internal auditory artery. Wave I of the BAEP's and the P1-N1 complex of the IAM-EAP's are important indicators of cochlear blood flow during surgical intervention. As possible causes of internal auditory artery obstruction, mechanical distortion of the relationship between the anterior inferior cerebellar artery (AICA) and the internal auditory artery at the junctional portion, mechanical vasospasm of the AICA-internal auditory artery complex, and ensuing no-reflow phenomena are discussed. Evoked action potentials are expected to be a useful intraoperative real-time monitor during CPA surgery that can detect rapid changes derived from cochlear artery insufficency. The real-time aspects can overcome some of the disadvantages of BAEP monitoring.

Time course of mossy fiber degeneration following pontine ablation in the rat.

The normal ultrastructure of mossy fiber terminals within the ansiform lobule of the rat was investigated in parasagittal sections of the cerebellar cortex. Four types of mossy fiber varicosities (simple and complex dispersed, simple and complex clustered) were distinguished on the basis of the presence or absence of clublike excrescences and the concentration of synaptic vesicles within the cortical zone of the terminal. Removal of the pontocerebellar input to the contralateral cerebellar hemisphere was performed electrolytically. Such lesions, when placed in the basilar pontine gray using a dorsal approach, resulted in the degeneration of nearly the entire population of mossy fiber varicosities within the contralateral ansiform lobule. As early as 3 days following pontine ablation, degenerative changes were observed within the synaptic portions of the mossy fibers. Two distinct axonal reactions were apparent within this population of degenerating varicosities. A small population of mossy fiber varicosities (12%) of the simple clustered variety underwent a rapid course of electron-dense degeneration, which was complete by the fifth day. These mossy fiber varicosities were very susceptible to phagocytosis by reactive glial elements. The second group which consisted of simple (60%) and complex (26%) varieties of dispersed terminals, underwent a very slow course of electron-dense degeneration. Reactive glial cells were rarely found in association with this second group of degenerating varicosities. As a result, most glomeruli were found to contain debris from degenerating mossy fiber varicosities throughout the first 57 days following pontine lesions. The majority of the cerebellar glomeruli, however, were denervated by 80 days.

Long-term effect of mossy fiber degeneration in the rat.

Mossy fiber-deafferentated rats (20) were permitted to survive from 34 to to 120 days and subsequently examined following Golgi-Cox preparation or after processing for electron microscopy. The primary response to mossy fiber deafferentation was transneuronal degeneration of the granule cell system. Morphological evidence is provided that suggests that the mossy fiber varicosity plays an important role in the fragmentation and removal of the granule cell digitiform dendrite. Computer-assisted image analysis of Golgi-impregnated Purkinje cells indicated significant losses in both smooth branch and spiny branchlet numbers following loss of the mossy fiber input. Ultrastructural examination revealed that a secondary transneuronal degeneration occurred within the dendritic arborization of both Purkinje cells and molecular layer interneurons. Although an overall reduction in the number of dendritic spines occurred along the terminal branchlets following mossy fiber deafferentation, several of the existing spines underwent marked changes in length, with some elongating to more than twice their size. By increasing the length of their spines, denervated Purkinje cells may acquire new synaptic contacts.

Early auditory evoked potentials (EAEPs) in the rabbit. Normative data and effects of lesions in the cerebello-pontine angle.

Early auditory evoked potentials (EAEPs) were measured in rabbits. After establishing normative data an operative method was developed to expose the cerebello-pontine angle. Compression of the VIIIth nerve and a reduction of blood supply to the cochlea via the labyrinthine artery altered the EAEP systematically. In all cases of an VIIIth nerve lesion wave 1 continued to be elicited whereas waves 2-5 disappeared. Circulatory disturbances had an effect upon wave 1. The results indicate that the generator of wave 1 is the unit cochlea/acoustic nerve and of waves 2-5 the auditory pathway within the brain stem. The resultant data help to understand wave alterations in patients with acoustic neuromas.

[Early auditory evoked potentials (EAEP) following cochlear nerve lesions in the cerebellopontile angle. An animal experiment study]. / Frühe akustisch evozierte Potentiale (FAEP) nach Läsionen des N. cochlearis im Kleinhirnbrückenwinkel. Eine tierexperimentelle Studie.

After exposure of the cerebello-pontine angle, various lesions were applied to the cochlear nerve in 20 rabbits. Changes of the EAEP were registered at the same time. Lesions proximal to the internal auditory meatus hardly exercised any influence on wave I. Waves II-V disappeared immediately after the trauma, Partial or complete recovery was observed, depending on the extension of the nerve lesion. Dissection or crushing of the cochlear nerve resulted in permanent disappearance of the waves II-V. Wave I often showed a slight reduction of amplitude, combined with a broadening of its duration and increase in latency. Lesions of minor intensity produced a transient disappearance of waves II-V. Recovery of these waves occurred within the following 2-3 days.

Brain-stem auditory-evoked potentials recorded directly from human brain-stem and thalamus.

Brain-stem auditory-evoked potentials were recorded in neurosurgical patients from surface electrodes applied to the VIIIth nerve, medulla, pons, midbrain and cortex; from depth electrodes in the thalamus; and from a movable electrode in the IVth, IIIrd, and lateral ventricles. The potentials recordable over the scalp within 10 ms after click stimulation are characterized by a slow positive wave (peaking at 5 to 6 ms) and a negative wave (8 to 10 ms) with 7 small positive wavelets superimposed upon them. The sources of these components have been identified by observing their increased amplitude in depth recordings, and by tracing the potentials from their intracranial maxima to the scalp. Wave I is generated within the most distal portion of the VIII nerve; Wave V in the midbrain (inferior colliculus); and Wave VI the medial geniculate body. Both low positive and negative components have their origins in the inferior colliculus. Intracranially-recorded brain-stem auditory-evoked potential showed very rapid changes in amplitude within the brain-stem but only slight changes in the more rostral regions, although their amplitude gradients varied in the different components. They also demonstrated minor but systematic shifts in latency with distance from the potential sources, reflecting a significant overlap of separate potentials. This effect must be taken into account in the interpretation of a 'concurrent' intracranial potential as the source of a far-field surface-recorded potential.