No postnatal doubling of number of neurons in human Broca’s areas (Brodmann areas 44 and 45)? A stereological study

Myeloarchitectonic Asymmetries of Language Regions in the Human Brain

One prominent theory in neuroscience and psychology assumes that cortical regions for language are left hemisphere lateralized in the human brain. In the current study, we used a novel technique, quantitative magnetic resonance imaging (qMRI), to examine interhemispheric asymmetries in language regions in terms of macromolecular tissue volume (MTV) and quantitative longitudinal relaxation time (T1) maps in the living human brain. These two measures are known to reflect cortical myeloarchitecture from the microstructural perspective. One hundred and fifteen adults (55 male, 60 female) were examined for their myeloarchitectonic asymmetries of language regions. We found that the cortical myeloarchitecture of inferior frontal areas including the pars opercularis, pars triangularis, and pars orbitalis is left lateralized, while that of the middle temporal gyrus, Heschl’s gyrus, and planum temporale is right lateralized. Moreover, the leftward lateralization of myelination structure is significantly correlated with language skills measured by phonemic and speech tone awareness. This study reveals for the first time a mixed pattern of myeloarchitectonic asymmetries, which calls for a general theory to accommodate the full complexity of principles underlying human hemispheric specialization.

Asymmetry in the Cytoarchitecture of the Area 44 Homolog of the Brain of the Chimpanzee Pan troglodytes

The evolution of the brain in apes and man followed a joint pathway stemming from common ancestors 5-10 million years ago. However, although apparently sharing similar organization and neurochemical properties, association areas of the isocortex remain one of the cornerstones of what sets humans aside from other primates. Brodmann's area 44, the area of Broca, is known for its implication in speech, and thus indirectly is a key mark of human uniqueness. This latero-caudal part of the frontal lobe shows a marked functional asymmetry in humans, and takes part in other complex functions, including learning and imitation, tool use, music and contains the mirror neuron system (MNS). Since the main features in the cytoarchitecture of Broca's area remains relatively constant in hominids, including in our closest relative, the chimpanzee Pan troglodytes, investigations on the finer structure, cellular organization, connectivity and eventual asymmetry of area 44 have a direct bearing on the understanding of the neural mechanisms at the base of our language. The semi-automated image analysis technology that we employed in the current study showed that the structure of the cortical layers of the chimpanzee contains elements of asymmetry that are discussed in relation to the corresponding human areas and the putative resulting disparity of function.

Curcumin prevents neuronal loss and structural changes in the superior cervical (sympathetic) ganglion induced by chronic sleep deprivation, in the rat model

Background

In modern societies, sleep deprivation is a serious health problem. This problem could be induced by a variety of reasons, including lifestyle habits or neurological disorders. Chronic sleep deprivation (CSD) could have complex biological consequences, such as changes in neural autonomic control, increased oxidative stress, and inflammatory responses. The superior cervical ganglion (SCG) is an important sympathetic component of the autonomic nervous system. CSD can lead to a wide range of neurological consequences in SCG, which mainly supply innervations to circadian system and other structures. As the active component of Curcuma longa, curcumin possesses many therapeutic properties; including neuroprotective. This study aimed to evaluate the effect of CSD on the SCG histomorphometrical changes and the protective effect of curcumin in preventing these changes.

Methods

Thirty-six male rats were randomly assigned to the control, curcumin, CSD, CSD + curcumin, grid floor control, and grid floor + curcumin groups. The CSD was induced by a modified multiple platform apparatus for 21 days and animals were sacrificed at the end of CSD or treatment, and their SCGs removed for stereological and TUNEL evaluations and also spatial arrangement of neurons in this structure.

Results

Concerning stereological findings, CSD significantly reduced the volume of SCG and its total number of neurons and satellite glial cells in comparison with the control animals (P < 0.05). Treatment of CSD with curcumin prevented these decreases. Furthermore, TUNEL evaluation showed significant apoptosis in the SCG cells in the CSD group, and treatment with curcumin significantly decreased this apoptosis (P < 0.01). This decrease in apoptosis was observed in all control groups that received curcumin. CSD also changed the spatial arrangement of ganglionic neurons into a random pattern, whereas treatment with curcumin preserved its regular pattern.

Conclusions

CSD could potentially induce neuronal loss and structural changes including random spatial distribution in the SCG neurons. Deleterious effects of sleep deprivation could be prevented by the oral administration of curcumin. Furthermore, the consumption of curcumin in a healthy person might lead to a reduction of cell death.

Coevolution in the timing of GABAergic and pyramidal neuron maturation in primates

The cortex of primates is relatively expanded compared with many other mammals, yet little is known about what developmental processes account for the expansion of cortical subtype numbers in primates, including humans. We asked whether GABAergic and pyramidal neuron production occurs for longer than expected in primates than in mice in a sample of 86 developing primate and rodent brains. We use high-resolution structural, diffusion MR scans and histological material to compare the timing of the ganglionic eminences (GE) and cortical proliferative pool (CPP) maturation between humans, macaques, rats, and mice. We also compare the timing of post-neurogenetic maturation of GABAergic and pyramidal neurons in primates (i.e. humans, macaques) relative to rats and mice to identify whether delays in neurogenesis are concomitant with delayed post-neurogenetic maturation. We found that the growth of the GE and CPP are both selectively delayed compared with other events in primates. By contrast, the timing of post-neurogenetic GABAergic and pyramidal events (e.g. synaptogenesis) are predictable from the timing of other events in primates and in studied rodents. The extended duration of GABAergic and pyramidal neuron production is associated with the amplification of GABAerigc and pyramidal neuron numbers in the human and non-human primate cortex.

Differential effect of lithium on cell number in the hippocampus and prefrontal cortex in adult mice: a stereological study

OBJECTIVES

Neuroimaging studies have revealed lithium-related increases in the volume of gray matter in the prefrontal cortex (PFC) and hippocampus. Postmortem human studies have reported alterations in neuronal and glial cell density and size in the PFC of lithium-treated subjects. Rodents treated with lithium exhibit cell proliferation in the dentate gyrus (DG) of the hippocampus. However, it is not known whether hippocampal and PFC volume are also increased in these animals or whether cell number in the PFC is altered.

METHODS

Using stereological methods, this study estimated the total numbers of neurons and glia, and the packing density of astrocytes in the DG and PFC of normal adult mice treated with lithium, and evaluated the total volume of these regions and the entire neocortex.

RESULTS

Lithium treatment increased the total numbers of neurons and glia in the DG (by 25% and 21%, respectively) and the density of astrocytes but did not alter total numbers in the PFC. However, the volumes of the hippocampus and its subfields, the PFC and its subareas, and the entire neocortex were not altered by lithium.

CONCLUSIONS

Both neuronal and glial cells accounted for lithium-induced cell proliferation in the DG. That the numbers of neurons and glia were unchanged in the PFC is consistent with the view that this region is not a neurogenic zone. Further studies are required to clarify the impact of lithium treatment on the PFC under pathological conditions and to investigate the dissociation between increased cell proliferation and unchanged volume in the hippocampus.

Stereological study of pyramidal neurons in the human superior temporal gyrus from childhood to adulthood

The association cortex of the superior temporal gyrus (STG) is implicated in complex social and linguistic functions. Thus, reliable methods for quantifying cellular variation in this region could greatly benefit researchers interested in addressing the cellular correlates of typical and atypical function associated with these critical cognitive abilities. To facilitate this task, we first present a general set of cytoarchitectonic criteria targeted specifically toward stereological analyses of thick, Nissl-stained sections for the homotypical cortex of the STG, referred to here as BA22/TA. Second, we use the optical fractionator to estimate pyramidal neuron number and the nucleator for pyramidal somal and nuclear volume. We also investigated the influence of age and sex on these parameters, as well as set a typically developing baseline for future comparisons. In 11 typically developing cases aged 4-48 years, the most distinguishing features of BA22/TA were the presence of distinct granular layers, a prominent, jagged layer IIIc, and a distinctly staining VIa. The average number of neurons was 91 ± 15 million, the volume of pyramidal soma 1,512 µm(3) , and the nuclear volume 348 µm(3) . We found no correlation with age and neuron number. In contrast, pyramidal somal and nuclear volume were both negatively correlated and linearly associated with age in regression analyses. We found no significant sex differences. Overall, the data support the idea that postnatal neuron numbers are relatively stable through development but also suggest that neuronal volume may be subject to important developmental variation. Both measures are critical variables in the study of developmental neuropathology.

GABA neuron alterations, cortical circuit dysfunction and cognitive deficits in schizophrenia

Schizophrenia is a brain disorder associated with cognitive deficits that severely affect the patients' capacity for daily functioning. Whereas our understanding of its pathophysiology is limited, postmortem studies suggest that schizophrenia is associated with deficits of GABA-mediated synaptic transmission. A major role of GABA-mediated transmission may be producing synchronized network oscillations which are currently hypothesized to be essential for normal cognitive function. Therefore, cognitive deficits in schizophrenia may result from a GABA synapse dysfunction that disturbs neural synchrony. Here, we highlight recent studies further suggesting alterations of GABA transmission and network oscillations in schizophrenia. We also review current models for the mechanisms of GABA-mediated synchronization of neural activity, focusing on parvalbumin-positive GABA neurons, which are altered in schizophrenia and whose function has been strongly linked to the production of neural synchrony. Alterations of GABA signaling that impair gamma oscillations and, as a result, cognitive function suggest paths for novel therapeutic interventions.

Parcellation in left lateral parietal cortex is similar in adults and children

A key question in developmental neuroscience involves understanding how and when the cerebral cortex is partitioned into distinct functional areas. The present study used functional connectivity MRI mapping and graph theory to identify putative cortical areas and generate a parcellation scheme of left lateral parietal cortex (LLPC) in 7 to 10-year-old children and adults. Results indicated that a majority of putative LLPC areas could be matched across groups (mean distance between matched areas across age: 3.15 mm). Furthermore, the boundaries of children's putative LLPC areas respected the boundaries generated from the adults' parcellation scheme for a majority of children's areas (13/15). Consistent with prior research, matched LLPC areas showed age-related differences in functional connectivity strength with other brain regions. These results suggest that LLPC cortical parcellation and functional connectivity mature along different developmental trajectories, with adult-like boundaries between LLPC areas established in school-age children prior to adult-like functional connectivity.

3-D cytoarchitectonic parcellation of human orbitofrontal cortex correlation with postmortem MRI

The orbitofrontal cortex (OFC) is located on the basal surface of the frontal lobe and is distinguished by its unique anatomical and functional features. Clinical and postmortem studies suggest the involvement of the orbitofrontal cortex in psychiatric disorders. However, the exact parcellation of this cortical region is still a matter of debate. Therefore, the goal of this study is to provide a detailed description of the extent of borders of individual orbitofrontal cortical areas using cytoarchitectonic criteria in a large sample of human brains, which could be applied by independent neuroanatomists. To make this microscopic parcellation useful to neuroimaging studies, magnetic resonance images of postmortem brains in the coronal plane were collected prior to the preparation of coronal histological sections from the same brains. A complete series of coronal sections from 6 normal human brains and partial sections from the frontal cortex of 21 normal human brains were stained with general histological and immunohistochemical methods specific for different cell-types. These sections were examined microscopically by two independent neuroanatomists (HBMU and GR) to achieve reproducible delineations. After the borders were determined, the tissue sections were superimposed on the corresponding magnetic resonance images. Based on our cytoarchitectonical criteria, Brodmann's areas 47 and 11 were included in the human orbitofrontal cortex. Area 47 was further subdivided into three medial (located on the medial, anterior and posterior orbital gyri) and two lateral (located on the lateral orbital gyrus) subareas. In addition, we observed an anterior-posterior gradient in the cytoarchitecture of areas 11 and 47. The transverse orbital sulcus corresponds roughly to the transition between the subregions of the anterior and posterior OFC. Finally, the present delineation is contrasted with an overview of the different published nomenclatures for the OFC parcellation.

The posterior parahippocampal gyrus is preferentially affected in age-related memory decline

Atrophy in the medial temporal lobe is generally considered to be highly associated with age-related memory decline. Volume loss in the hippocampus and entorhinal cortex has extensively been investigated, but the posterior parts of the parahippocampal gyrus have received little attention. The present MRI study investigated whether volume differences in medial temporal lobe areas are differentially related to age-related memory decline. Thirty-nine subjects from a longitudinal study on cognitive aging (the Maastricht Aging Study) have been examined: 20 participants (mean age=67 years, range 52-80) with memory decline over a period of 12 years were matched to 19 participants without memory decline. Manual tracing was performed on 3T MR images to measure the volumes of the anterior, middle and posterior parts of the hippocampus and parahippocampal gyrus. A robust group difference and a significant association with memory decline were observed only in the posterior part of the parahippocampal gyrus. Our results may suggest that the posterior parahippocampal gyrus plays a key role in age-related memory decline.

Broca's area: nomenclature, anatomy, typology and asymmetry

In this review, we (i) describe the nomenclature of Broca's area and show how the circumscribed definition of Broca's area is disassociated from Broca's aphasia, (ii) describe in detail how the gross anatomy of Broca's area varies between people, and how the definitions vary between studies, (iii) attempt to reconcile the findings of structural asymmetry of Broca's area with the differences in methodological approaches, (iv) consider the functional significance of cytoarchitectonic definitions of Broca's area, and (v) critically elucidate the significance of circumscribed regions of cortex for language lateralisation and language development. Contrary to what has previously been reported in the literature, asymmetry of Broca's area has not been reproducibly demonstrated, particularly on a gross morphological level. This may be due to major inconsistencies in methodology (including different anatomical boundaries, measurement techniques and samples studied) or that the sulcal contours defining Broca's area are so naturally variable between people making a standard definition difficult. Cytoarchitectonic analyses more often than not report leftward asymmetry of some component of area 44 and/or area 45. If a structural asymmetry of Broca's area does exist, it is variable, which differs from that of the functional asymmetry of language, which is more consistent. One reason for this might be that the link between cellular architecture, connectivity and language function still remains to be elucidated. There is currently no convincing explanation to associate asymmetry of Broca's area with the lateralisation of language.

Prefrontal cortex atrophy predicts dementia over a six-year period

The present study investigated prefrontal cortex (PFC) atrophy as a possible predictor of dementia. Eighty-eight older participants of the Maastricht Aging Study (MAAS) were administered for neuropsychological tests at baseline and after three years (t(3)). Magnetic resonance images were acquired at t(3) and nine years after baseline all participants were screened for dementia. Three groups were distinguished: (1) participants who did not develop dementia or cognitive decline, (2) participants who did not develop dementia but did show significant cognitive decline, and (3) participants who developed dementia. Gray matter volume of structures in the PFC and medial temporal lobe (MTL) was measured. Prefrontal volume was significantly smaller in group 3 than in the other two groups, and PFC volume was significantly better than MTL volume in distinguishing between groups 2 and 3. These findings suggest that PFC atrophy is highly associated with dementia and can be considered an important predictor of the disease. It may even be a better predictor than the MTL atrophy that has been found in earlier studies.

Adult structure and development of the human fronto-opercular cerebral cortex (Broca's region)

Broca's area encompasses opercular and triangular part of the inferior frontal gyrus, covered by Brodmann's areas 44 and 45, respectively. Recent neuroimaging studies have revealed that, in addition to classical language functions, Broca's area has novel and unexpected functions, serving as a likely interface of action and perception important for both verbal and nonverbal communication. In this review, we focus on structural features of Broca's area in adult and developing human brain. We emphasize that: (a) in terms of architectonic classification, Broca's area displays a dual nature by virtue of its intermediate position between agranular motor-premotor cortex and granular prefrontal associative cortex; and (b) numerous studies of morphological asymmetries are of limited value for understanding neurobiological basis of functions implemented by Broca's area. Finally, we summarize findings from our ongoing study on postnatal development of two defining cytoarchitectonic features of Broca's area in the adult brain, magnopyramidality (meaning that pyramidal neurons in layer III are larger than those in layer V) and dysgranularity (meaning that cortical layer IV is present, but poorly developed). We conclude that areal specification of areas 44 and 45 requires at least 2 (and probably 3) years of postnatal life for its gradual completion.

Sulcal variability, stereological measurement and asymmetry of Broca's area on MR images

Leftward volume asymmetry of the pars opercularis and pars triangularis may exist in the human brain, frequently referred to as Broca's area, given the functional asymmetries observed in this region with regard to language expression. However, post-mortem and magnetic resonance imaging (MRI) studies have failed to consistently identify such a volumetric asymmetry. In the present study, an analysis of the asymmetry of sulco-gyral anatomy and volume of this anterior speech region was performed in combination with an analysis of the morphology and volume asymmetry of the planum temporale, located within the posterior speech region, in 50 healthy subjects using MRI. Variations in sulcal anatomy were documented according to strict classification schemes and volume estimation of the grey matter within the brain structures was performed using the Cavalieri method of stereology. Results indicated great variation in the morphology of and connectivity between the inferior frontal, inferior precentral and diagonal sulci. There were significant inter-hemispheric differences in the presence of (1) the diagonal sulcus within the pars opercularis, and (2) horizontal termination of the posterior Sylvian fissure (relative to upward oblique termination), both with an increased leftward incidence. Double parallel inferior precentral sulci and absent anterior rami of the Sylvian fissure prevented stereological measurements in five subjects. Therefore volumes were obtained from 45 subjects. There was a significant leftward volume asymmetry of the pars opercularis (P = 0.02), which was significantly related to the asymmetrical presence of the diagonal sulcus (P < 0.01). Group-wise pars opercularis volume asymmetry did not exist when a diagonal sulcus was present in both or neither hemispheres. There was no significant volume asymmetry of the pars triangularis. There was a significant leftward volume asymmetry of the planum temporale (P < 0.001), which was significantly associated with the shape of the posterior Sylvian fissure as a unilateral right or left upward oblique termination was always associated with leftward or rightward volume asymmetry respectively (P < 0.01). There was no relationship between volume asymmetries of the anterior and posterior speech regions. Our findings illustrate the extent of morphological variability of the anterior speech region and demonstrate the difficulties encountered when determining volumetric asymmetries of the inferior frontal gyrus, particularly when sulci are discontinuous, absent or bifid. When the intrasulcal grey matter of this region is exhaustively sampled according to strict anatomical landmarks, the volume of the pars opercularis is leftward asymmetrical. This manuscript illustrates the importance of simultaneous consideration of brain morphology and morphometry in studies of cerebral asymmetry.

Lifespan Alterations of Basal Dendritic Trees of Pyramidal Neurons in the Human Prefrontal Cortex: A Layer-Specific Pattern

The postnatal development and lifespan alterations in basal dendrites of large layer IIIC and layer V pyramidal neurons were quantitatively studied. Both classes of neurons were characterized by rapid dendritic growth during the first postnatal months. At birth, layer V pyramidal neurons had larger and more complex dendritic trees than those of layer IIIC; however, at 1 postnatal month both classes of neurons displayed a similar extent of dendritic outgrowth. In addition, after a more than year-long "dormant" period of only fine dendritic rearrangement, layer IIIC pyramidal neurons displayed a second period of dendritic growth, starting at the end of the second year and continuing in the third year. During that period, the dendritic tree of layer IIIC pyramidal neurons became more extensive than that of layer V pyramidal neurons. Thus, layer IIIC pyramidal neurons appear to show a biphasic pattern of postnatal dendritic development. Furthermore, the childhood period was characterized by transient increase in size of pyramidal cell somata, which was more pronounced for neurons in layer IIIC. These structural changes occurred during both the period of rapid cognitive development in preschool children and the period of protracted cognitive maturation during the childhood, puberty, and adolescence.

A comprehensive assessment of gray and white matter volumes and their relationship to outcome and severity in schizophrenia

Preliminary data suggest an association of posterior cortical gray matter reduction with poor outcome in schizophrenia. We made a systematic MRI assessment of regional gray and white matter volumes, parcellated into 40 Brodmann's areas, in 104 patients with schizophrenia (51 with good outcomes, 53 with poor outcomes) and 41 normal comparison subjects, and investigated correlations of regional morphometry with outcome and severity of the illness. Schizophrenia patients displayed differential reductions in frontal and to a lesser degree temporal gray matter volumes in both hemispheres, most pronounced in the frontal pole and lateral temporal cortex. White matter volumes in schizophrenia patients were bilaterally increased, primarily in the frontal, parietal, and isolated temporal regions, with volume reductions confined to anterior cingulate gyrus. In patients with schizophrenia as a group, higher illness severity was associated with reduced temporal gray matter volumes and expanded frontal white matter volumes in both hemispheres. In comparison to good-outcome group, patients with poor outcomes had lower temporal, occipital, and to a lesser degree parietal gray matter volumes in both hemispheres and temporal, parietal, occipital, and posterior cingulate white matter volumes in the right hemisphere. While gray matter deficits in the granular cortex were observed in all schizophrenia patients, agranular cortical deficits in the left hemisphere were peculiar to patients with poor outcomes. These results provide support for frontotemporal gray matter reduction and frontoparietal white matter expansion in schizophrenia. Poor outcome is associated with more posterior distribution (posteriorization) of both gray and white matter changes, and with preferential impairment in the unimodal visual and paralimbic cortical regions.

Total number of neurons in the habenular nuclei of the rat epithalamus: a stereological study

The total number of neurons in the medial and lateral habenular nuclei of the rat epithalamus was estimated using modern stereological counting methods and systematic random sampling techniques. Six to eight young adult male rats, and a complete set of serial 40-microm glycolmethacrylate sections for each rat, were used to quantify neuronal numbers. After a random start, a systematic subset (e.g. every third) of the serial sections was used to estimate the total volume of each nucleus using Cavalieri's method. The same set of sampled sections was used to estimate the number of neurons in a known subvolume (i.e. the numerical density N(v)) by the optical disector method. Multiplication of the total volume by N(v) yielded the total number of neurons. It was found that the right medial habenular nucleus consisted, on average, of 18,000 neurons (with a coefficient of variation of 0.18), while the right lateral habenular nucleus had 13,000 neurons on average (0.14). These total neuronal numbers provide important data for the transfer of information through these nuclei and for species comparisons.

Association of umbilical cord blood lead with neonatal behavior at varying levels of exposure

Background

In the light of the ongoing debate about lowering the cut-off for acceptable blood lead level to <5 μg/dL from the currently recommended level of <10 μg/dL, we considered whether prenatal exposure to varying levels of lead is associated with similar or disparate effects on neonatal behavior.

Methods

Using Brazelton's Neonatal Behavioral Assessment Scale (NBAS), an epidemiological approach and robust statistical techniques like multivariate linear regression, logistic regression, Poisson regression and structural equations modeling analyses we estimated the simultaneous indirect effects of umbilical cord blood lead (CBL) levels and other neonatal covariates on the NBAS clusters.

Results

We observed that when analyzed in all study subjects, the CBL levels independently and strongly influenced autonomic stability and abnormal reflexes clusters. However, when the analysis was restricted to neonates with CBL <10 μg/dL, CBL levels strongly influenced the range of state, motor and autonomic stability clusters. Abnormal walking reflex was consistently associated with an increased CBL level irrespective of the cut-off for CBL, however, only at the lower cut-offs were the predominantly behavioral effects of CBL discernible.

Conclusion

Our results further endorse the need to be cognizant of the detrimental effects of blood lead on neonates even at a low-dose prenatal exposure.