Vertical bias in dendritic trees of non-pyramidal neocortical neurons expressing GAD67-GFP in vitro

Application of the mirror technique for block-face scanning electron microscopy

The mirror technique adapted for electron microscopy allows correlating neuronal structures across the cutting plane of adjoining light microscopic sections which, however, have a limited thickness, typically less than 100 µm (Talapka et al. in Front Neuroanat, 2021, 10.3389/fnana.2021.652422). Here, we extend the mirror technique for tissue blocks in the millimeter range and demonstrate compatibility with serial block-face electron microscopy (SBEM). An essential step of the methodological improvement regards the recognition that unbound resin must be removed from the tissue surface to gain visibility of surface structures. To this, the tissue block was placed on absorbent paper during the curing process. In this way, neuronal cell bodies could be unequivocally identified using epi-illumination and confocal microscopy. Thus, the layout of cell bodies which were cut by the sectioning plane can be correlated with the layout of their complementary part in the adjoining section processed for immunohistochemistry. The modified mirror technique obviates the spatial limit in investigating synaptology of neurochemically identified structures such as neuronal processes, dendrites and axons.

New insights into cortical interneurons development and classification: contribution of developmental studies

The concerted development of GABAergic interneurons and glutamatergic neurons is a key feature in the construction of the cerebral cortex. In contrast with glutamatergic neurons, GABAergic interneurons are heterogeneous differing by their axonal and dendritic morphologies, biochemical markers, connectivity, and physiology. Furthermore, interneurons have recently been shown to be generated in a variety of telencephalic structures (the ganglionic eminences, the entopeduncular and preoptic areas and the cortex). This review describes the origin, specification and differentiation of interneurons. These recent developmental studies may help to clarify the classification of mature interneurons. In particular recent studies, including our own, provide compelling evidences that most interneurons are specify after their last division in their region of origin before migration. The roles of target tissues in determining the final physiological properties of interneurons are also discussed.

Classification of NPY-expressing neocortical interneurons

Neuropeptide Y (NPY) is an abundant neuropeptide of the neocortex involved in numerous physiological and pathological processes. Because of the large electrophysiological, molecular, and morphological diversity of NPY-expressing neurons their precise identity remains unclear. To define distinct populations of NPY neurons we characterized, in acute slices of rat barrel cortex, 200 cortical neurons of layers I-IV by means of whole-cell patch-clamp recordings, biocytin labeling, and single-cell reverse transcriptase-PCR designed to probe for the expression of well established molecular markers for cortical neurons. To classify reliably cortical NPY neurons, we used and compared different unsupervised clustering algorithms based on laminar location and electrophysiological and molecular properties. These classification schemes confirmed that NPY neurons are nearly exclusively GABAergic and consistently disclosed three main types of NPY-expressing interneurons. (1) Neurogliaform-like neurons exhibiting a dense axonal arbor, were the most frequent and superficial, and substantially expressed the neuronal isoform of nitric oxide synthase. (2) Martinotti-like cells characterized by an ascending axon ramifying in layer I coexpressed somatostatin and were the most excitable type. (3) Among fast-spiking and parvalbumin-positive basket cells, NPY expression was correlated with pronounced spike latency. By clarifying the diversity of cortical NPY neurons, this study establishes a basis for future investigations aiming at elucidating their physiological roles.

Viral vectors based on bidirectional cell-specific mammalian promoters and transcriptional amplification strategy for use in vitro and in vivo

BACKGROUND

Using cell-type-specific promoters to restrict gene expression to particular cells is an attractive approach for gene therapy, but often hampered by insufficient transcriptional activity of these promoters. Previous studies have shown that transcriptional amplification strategy (TAS) can be used to enhance the activity of such promoters without loss of cell type specificity. Originally TAS involved the use of two copies of a cell-specific promoter leading to generation of large expression cassettes, which can be hard to use given the space limitations of the conventional viral gene expression vectors.

RESULTS

We have now developed a new bidirectional lentiviral vector system, based on TAS that can enhance the transcriptional activity of human synapsin-1 (SYN) promoter and the compact glial fibrillary acidic protein (GfaABC1D) promoter. In the opposite orientation, a minimal core promoter (65 bp) derived from the human cytomegalovirus (CMV) was joined upstream of the SYN promoter or GfaABC1D promoter. This led to the formation of synthetic bidirectional promoters which were flanked with two gene expression cassettes. The 5' cassette transcribed the artificial transcriptional activator. The downstream cassette drove the synthesis of the gene of interest. Studies in both cell cultures and in vivo showed that the new bidirectional promoters greatly increased the expression level of the reporter gene. In vivo studies also showed that transgene expression was enhanced without loss of cell specificity of both SYN and GfaABC1D promoters.

CONCLUSION

This work establishes a novel approach for creating compact TAS-amplified cell-specific promoters, a feature important for their use in viral backbones. This improved approach should prove useful for the development of powerful gene expression systems based on weak cell-specific promoters.

A neuroanatomically grounded Hebbian-learning model of attention-language interactions in the human brain

Meaningful familiar stimuli and senseless unknown materials lead to different patterns of brain activation. A late major neurophysiological response indexing ‘sense’ is the negative component of event-related potential peaking at around 400 ms (N400), an event-related potential that emerges in attention-demanding tasks and is larger for senseless materials (e.g. meaningless pseudowords) than for matched meaningful stimuli (words). However, the mismatch negativity (latency 100–250 ms), an early automatic brain response elicited under distraction, is larger to words than to pseudowords, thus exhibiting the opposite pattern to that seen for the N400. So far, no theoretical account has been able to reconcile and explain these findings by means of a single, mechanistic neural model. We implemented a neuroanatomically grounded neural network model of the left perisylvian language cortex and simulated: (i) brain processes of early language acquisition and (ii) cortical responses to familiar word and senseless pseudoword stimuli. We found that variation of the area-specific inhibition (the model correlate of attention) modulated the simulated brain response to words and pseudowords, producing either an N400- or a mismatch negativity-like response depending on the amount of inhibition (i.e. available attentional resources). Our model: (i) provides a unifying explanatory account, at cortical level, of experimental observations that, so far, had not been given a coherent interpretation within a single framework; (ii) demonstrates the viability of purely Hebbian, associative learning in a multilayered neural network architecture; and (iii) makes clear predictions on the effects of attention on latency and magnitude of event-related potentials to lexical items. Such predictions have been confirmed by recent experimental evidence.

Development of GABA innervation in the cerebral and cerebellar cortices

In many areas of the vertebrate brain, such as the cerebral and cerebellar cortices, neural circuits rely on inhibition mediated by GABA (gamma-aminobutyric acid) to shape the spatiotemporal patterns of electrical signalling. The richness and subtlety of inhibition are achieved by diverse classes of interneurons that are endowed with distinct physiological properties. In addition, the axons of interneurons display highly characteristic and class-specific geometry and innervation patterns, and thereby distribute their output to discrete spatial domains, cell types and subcellular compartments in neural networks. The cellular and molecular mechanisms that specify and modify inhibitory innervation patterns are only just beginning to be understood.

The underside of the cerebral cortex: layer V/VI spiny inverted neurons

This paper presents an account of past and current research on spiny inverted neurons--alternatively also known as 'inverted pyramidal neurons'--in rats, rabbits and cats. In our laboratory, we have studied these cells with a battery of techniques suited for light and electron microscopy, including Nissl staining, Golgi impregnation, dye intracellular filling and axon retrograde track-tracing. Our results show that spiny inverted neurons make up less than 8.5 and 5.5% of all cortical neurons in the primary and secondary rabbit visual cortex, respectively. Infragranular spiny inverted neurons constitute 15 and 8.5% of infragranular neurons in the same animal and areas. Spiny inverted neurons congregate at layers V-VI in all studied species. Studies have also revealed that spiny inverted neurons are excitatory neurons which furnish axons for various cortico-cortical, cortico-claustral and cortico-striatal projections, but not for non-telencephalic centres such as the lateral and medial geniculate nuclei, the colliculi or the pons. As a group, each subset of inverted cells contributing to a given projection is located below the pyramidal neurons whose axons furnish the same centre. Spiny inverted neurons are particularly conspicuous as a source of the backward cortico-cortical projection to primary visual cortex and from this to the claustrum. Indeed, they constitute up to 82% of the infragranular cells that furnish these projections. Spiny inverted neurons may be classified into three subtypes according to the point of origin of the axon on the cell: the somatic basal pole which faces the cortical outer surface, the somatic flank and the reverse apical dendrite. As seen with electron microscopy, the axon initial segments of these subtypes are distinct from one another, not only in length and thickness, but also in the number of received synaptic boutons. All of these anatomical features together may support a synaptic-input integration which is peculiar to spiny inverted neurons. In this way, two differently qualified streams of axonal output may coexist in a projection which arises from a particular infragranular point within a given cortical area; one stream would be furnished by the typical pyramidal neurons, whereas spiny inverted neurons would constitute the other source of distinct information flow.

Glutamatergic or GABAergic neuron-specific, long-term expression in neocortical neurons from helper virus-free HSV-1 vectors containing the phosphate-activated glutaminase, vesicular glutamate transporter-1, or glutamic acid decarboxylase promoter

Many potential uses of direct gene transfer into neurons require restricting expression to one of the two major types of forebrain neurons, glutamatergic or GABAergic neurons. Thus, it is desirable to develop virus vectors that contain either a glutamatergic or GABAergic neuron-specific promoter. The brain/kidney phosphate-activated glutaminase (PAG), the product of the GLS1 gene, produces the majority of the glutamate for release as neurotransmitter, and is a marker for glutamatergic neurons. A PAG promoter was partially characterized using a cultured kidney cell line. The three vesicular glutamate transporters (VGLUTs) are expressed in distinct populations of neurons, and VGLUT1 is the predominant VGLUT in the neocortex, hippocampus, and cerebellar cortex. Glutamic acid decarboxylase (GAD) produces GABA; the two molecular forms of the enzyme, GAD65 and GAD67, are expressed in distinct, but largely overlapping, groups of neurons, and GAD67 is the predominant form in the neocortex. In transgenic mice, an approximately 9 kb fragment of the GAD67 promoter supports expression in most classes of GABAergic neurons. Here, we constructed plasmid (amplicon) Herpes Simplex Virus (HSV-1) vectors that placed the Lac Z gene under the regulation of putative PAG, VGLUT1, or GAD67 promoters. Helper virus-free vector stocks were delivered into postrhinal cortex, and the rats were sacrificed 4 days or 2 months later. The PAG or VGLUT1 promoters supported approximately 90% glutamatergic neuron-specific expression. The GAD67 promoter supported approximately 90% GABAergic neuron-specific expression. Long-term expression was observed using each promoter. Principles for obtaining long-term expression from HSV-1 vectors, based on these and other results, are discussed. Long-term glutamatergic or GABAergic neuron-specific expression may benefit specific experiments on learning or specific gene therapy approaches. Of note, promoter analyses might identify regulatory elements that determine a glutamatergic or GABAergic neuron.

Dendritic architecture of the von Economo neurons

The von Economo neurons are one of the few known specializations to hominoid cortical microcircuitry. Here, using a Golgi preparation of a human postmortem brain, we describe the dendritic architecture of this unique population of neurons. We have found that, in contrast to layer 5 pyramidal neurons, the von Economo neurons have sparse dendritic trees and symmetric apical and basal components. This result provides the first detailed anatomical description of a neuron type unique to great apes and humans.

Distinct subtypes of somatostatin-containing neocortical interneurons revealed in transgenic mice

GABA-releasing inhibitory interneurons in the cerebral cortex can be classified by their neurochemical content, firing patterns, or axonal targets, to name the most common criteria, but whether classifications using different criteria converge on the same neuronal subtypes, and how many such subtypes exist, is a matter of much current interest and considerable debate. To address these issues, we generated transgenic mice expressing green fluorescent protein (GFP) under control of the GAD67 promoter. In two of these lines, named X94 and X98, GFP expression in the barrel cortex was restricted to subsets of somatostatin-containing (SOM+) GABAergic interneurons, similar to the previously reported "GIN" line (Oliva et al., 2000), but the laminar distributions of GFP-expressing (GFP+) cell bodies in the X94, X98, and GIN lines were distinct and nearly complementary. We compared neurochemical content and axonal distribution patterns of GFP+ neurons among the three lines and analyzed in detail electrophysiological properties in a dataset of 150 neurons recorded in whole-cell, current-clamp mode. By all criteria, there was nearly perfect segregation of X94 and X98 GFP+ neurons, whereas GIN GFP+ neurons exhibited intermediate properties. In the X98 line, GFP expression was found in infragranular, calbindin-containing, layer 1-targeting ("Martinotti") cells that had a propensity to fire low-threshold calcium spikes, whereas X94 GFP+ cells were stuttering interneurons with quasi fast-spiking properties, residing in and targeting the thalamo-recipient neocortical layers. We conclude that much of the variability previously attributed to neocortical SOM+ interneurons can be accounted for by their natural grouping into distinct subtypes.

Differential expression of NMDA receptor subunits between neurons containing and not containing enkephalin in the mouse embryo spinal cord

We transfected cultures of mouse spinal cord slices with the enhanced green fluorescent protein (GFP) gene driven by the promoter for preproenkephalin, using the particle-mediated gene transfer system adapted for small neurons in the superficial dorsal horn, and observations were made after 4-6 days in vitro. A considerable number of cells in the superficial dorsal horn were observed to express GFP fluorescence, reminiscent of the previously reported distribution of enkephalinergic neurons in the spinal cord. The number of GFP-expressing neurons increased in response to forskolin application. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of single neurons revealed that the N-methyl-d-aspartate (NMDA) receptor NR2B subunit is expressed more frequently in enkephalinergic neurons, and the NR2A subunit more frequently in non-enkephalinergic neurons. These observations suggest that expression of NMDA receptor subunits is controlled differentially in distinct populations of neurochemically identified neurons in the spinal cord. Biolistic particle-mediated gene transfection seems useful for identifying neuronal phenotypes in organotypic cultures of the spinal cord.

Dendritic branch typing and spine expression patterns in cortical nonpyramidal cells

To understand the dendritic differentiation in various types of cortical nonpyramidal cells, we analyzed quantitatively their dendritic branching and spine expression. The dendritic internode and interspine interval obeyed exponential distributions with type-specific decay constants. The initial branching pattern, internode interval and spine density at the light microscopic level divided nonpyramidal cells into three dendritic types, correlated with axonal, neurochemical and firing types. The initial branching pattern determined the overall vertical spread of dendrites. Basket cell subtypes with different firing and chemical expression patterns were distinct in the vertical and horizontal spatial spread, providing diverse input territories. Internode densities of dendritic spines, as well as those of axonal synaptic boutons, did not correlate with the tortuosities and intervals, suggesting a tendency to distribute synapses homogeneously over the arbor. Dendritic spines identified at the electron microscopic level were different in length and shape among subtypes. Although the density was lower than that of pyramidal cells, spines themselves were also composed of several morphological types such as mushroom and multihead ones, which were expressed differentially among subtypes. Correlation of dendritic branching characteristics with differences in spine structure suggests distinct ways to receive specific inputs among the subtypes.

High-throughput morphometric analysis of individual neurons

To facilitate high-throughput quantitative analysis of neuronal structure, this study optimized the diOlistic method of whole neuron labeling to examine multiple neurons in fixed brain, and optimized image acquisition parameters to preserve signal for subsequent photoconversion. Fluorescent dye-coated gold particles were successively delivered by helium-powered ejection to 250 microm thick brain slices with loading density and penetration depth optimized to maximize the yield of labeled neurons within the slice while avoiding overlapping labeled dendritic processes in the x-y plane and z-axis. Labeled neurons were imaged using confocal laser-scanning microscopy with pinhole aperture and scan speed enhanced to minimize capture time and fluorescence degradation. Optimized image acquisition parameters preserved fluorescence signal and facilitated subsequent oxygen-enriched photoconversion for higher magnification dendritic spine analysis. Sampling criteria limited analysis to neurons whose z-axis dendritic processes were fully contained within the tissue slice and in which dye transport extended to the most distal portions of the dendrites. The yield of completely labeled neurons was, on average, more than 20 cells per brain region per animal. With optimized spatio-temporal diOlistic loading parameters, along with image acquisition parameters optimized for subsequent photoconversion, the present protocol provides a high-throughput strategy for full-scale quantitative analysis of three-dimensional neuronal morphology.

Viral vectors as tools for studies of central cardiovascular control

During the last few years physiological genomics has been the most rapidly developing area of physiology. Given the current ease of obtaining information about nucleotide sequences found in genomes and the vast amount of readily available clones, one of the most pertinent tasks is to find out about the roles of the individual genes and their families under normal and pathological conditions. Viral gene delivery into the brain is a powerful tool, which can be used to address a wide range of questions posed by physiological genomics including central nervous mechanisms regulating the cardio-vascular system. In this paper, we will give a short overview of current data obtained in this field using viral vectors and then look critically at the technology of viral gene transfer.

Disruption in the inhibitory architecture of the cell minicolumn: implications for autism

The modular arrangement of the neocortex is based on the cell minicolumn: a self-contained ecosystem of neurons and their afferent, efferent, and interneuronal connections. The authors' preliminary studies indicate that minicolumns in the brains of autistic patients are narrower, with an altered internal organization. More specifically, their minicolumns reveal less peripheral neuropil space and increased spacing among their constituent cells. The peripheral neuropil space of the minicolumn is the conduit, among other things, for inhibitory local circuit projections. A defect in these GABAergic fibers may correlate with the increased prevalence of seizures among autistic patients. This article expands on our initial findings by arguing for the specificity of GABAergic inhibition in the neocortex as being focused around its mini- and macrocolumnar organization. The authors conclude that GABAergic interneurons are vital to proper minicolumnar differentiation and signal processing (e.g., filtering capacity of the neocortex), thus providing a putative correlate to autistic symptomatology.

Developmental expression of matrix metalloproteinases 2 and 9 and their potential role in the histogenesis of the cerebellar cortex

The development of the cerebellar cortex depends on intrinsic genetic programs and orchestrated cell-cell/cell-matrix interactions. Matrix metalloproteinases (MMPs) are proteolytic enzymes that play an important role in these interactions. MMP-2 and MMP-9 are involved in diverse neuronal functions including migration, process extension, and synaptic plasticity. We investigated the spatiotemporal pattern of expression/activity of MMP-2/MMP-9 in the developing cerebellum and their role in the histogenesis of the cerebellar cortex. The levels of transcripts of MMP-2/MMP-9 were measured with real-time quantitative polymerase chain reaction. An initial decrease in MMP-2/MMP-9 transcripts was observed between postnatal days 3 (PD3) and PD6, and the mRNA levels remained relatively constant thereafter. Zymographic analysis revealed that the expression/activity of MMP-2/MMP-9 persisted longer than their transcripts; the downregulation occurred around PD9, suggesting a mechanism of translational or post-translational regulation. The gelatinase activity was localized in the external granule layer (EGL) and the internal granule layer during PD3-PD12. The immunoreactivity of MMP-2 was mainly localized in the EGL, the Bergmann glial fibers, and the Purkinje cell layer (PCL), whereas MMP-9 immunoreactivity was detected intensively in the PCL and the extracellular space of the molecular layer. Expression of MMP-9 was relatively weak in the EGL. The immunoreactivity of MMP-2/MMP-9 became undetectable after PD21. A similar expression pattern of MMP-2/MMP-9 was observed in organotypic cerebellar slice cultures. Exposure of organotypic slices to a specific MMP-2/MMP-9 inhibitor significantly increased the thickness of the EGL and concurrently decreased the number of migrating granule neurons in the molecular layer. Thus, MMP-2 and MMP-9 play a role in the postnatal cerebellar morphogenesis.

Brain-derived neurotrophic factor mediates activity-dependent dendritic growth in nonpyramidal neocortical interneurons in developing organotypic cultures

Brain-derived neurotrophic factor (BDNF) promotes postnatal maturation of GABAergic inhibition in the cerebral and cerebellar cortices, and its expression and release are enhanced by neuronal activity, suggesting that it acts in a feedback manner to maintain a balance between excitation and inhibition during development. BDNF promotes differentiation of cerebellar, hippocampal, and neostriatal inhibitory neurons, but its effects on the dendritic development of neocortical inhibitory interneurons remain unknown. Here, we show that BDNF mediates depolarization-induced dendritic growth and branching in neocortical interneurons. To visualize inhibitory interneurons, we biolistically transfected organotypic cortical slice cultures from neonatal mice with green fluorescent protein (GFP) driven by the glutamic acid decarboxylase (GAD)67 promoter. Nearly all GAD67-GFP-expressing neurons were nonpyramidal, many contained GABA, and some expressed markers of neurochemically defined GABAergic subtypes, indicating that GAD67-GFP-expressing neurons were GABAergic. We traced dendritic trees from confocal images of the same GAD67-GFP-expressing neurons before and after a 5 d growth period, and quantified the change in total dendritic length (TDL) and total dendritic branch points (TDBPs) for each neuron. GAD67-GFP-expressing neurons growing in control medium exhibited a 20% increase in TDL, but in 200 ng/ml BDNF or 10 mm KCl, this increase nearly doubled and was accompanied by a significant increase in TDBPs. Blocking action potentials with TTX did not prevent the BDNF-induced growth, but antibodies against BDNF blocked the growth-promoting effect of KCl. We conclude that BDNF, released by neocortical pyramidal neurons in response to depolarization, enhances dendritic growth and branching in nearby inhibitory interneurons.

Physiological, anatomical and genetic identification of CPG neurons in the developing mammalian spinal cord

The basic motor patterns underlying rhythmic limb movements during locomotion are generated by neuronal networks located within the spinal cord. These networks are called Central Pattern Generators (CPGs). Isolated spinal cord preparations from newborn rats and mice have become increasingly important for understanding the organization of the CPG in the mammalian spinal cord. Early studies using these preparations have focused on the overall network structure and the localization of the CPG. In this review we concentrate on recent experiments aimed at identifying and characterizing CPG-interneurons in the rodent. These experiments include the organization and function of descending commissural interneurons (dCINs) in the hindlimb CPG of the neonatal rat, as well as the role of Ephrin receptor A4 (EphA4) and its Ephrin ligand B3 (EphrinB3), in the construction of the mammalian locomotor network. These latter experiments have defined EphA4 as a molecular marker for mammalian excitatory hindlimb CPG neurons. We also review genetic approaches that can be applied to the mouse spinal cord. These include methods for identifying sub-populations of neurons by genetically encoded reporters, techniques to trace network connectivity with cell-specific genetically encoded tracers, and ways to selectively ablate or eliminate neuron populations from the CPG. We propose that by applying a multidisciplinary approach it will be possible to understand the network structure of the mammalian locomotor CPG. Such an understanding will be instrumental in devising new therapeutic strategies for patients with spinal cord injury.

The spatial dimensions of electrically coupled networks of interneurons in the neocortex

Inhibitory interneurons of the neocortex are electrically coupled to cells of the same type through gap junctions. We studied the spatial organization of two types of interneurons in the rat somatosensory cortex: fast-spiking (FS) parvalbumin-immunoreactive (PV+) cells, and low threshold-spiking (LTS) somatostatin-immunoreactive (SS+) cells. Paired recordings in layer 4 demonstrated that both the probability of coupling and the coupling coefficient drop steeply with intersomatic distance, reaching zero beyond 200 microm. The dendritic arbors of FS and LTS cells were reconstructed from electrophysiologically characterized, biocytin-filled cells; the two cell types had only minor differences in the number and span of their dendrites. However, there was a markedly higher density of PV+ cells than SS+ cells. PV+ cells were densest in layer 4, while SS+ cell density peaked in the subgranular layers. From these data we estimate that there is measurable electrical coupling (directly or indirectly via intermediary cells) between each interneuron and 20-50 others. The large number of electrical synapses implies that each interneuron participates in a large, continuous syncytium. To evaluate the functional significance of these findings, we examined several simple architectures of coupled networks analytically. We present a mathematical method to estimate the average summated coupling conductance that each cell receives from all of its neighbors, and the average leak conductance of individual cells, and we suggest that these have the same order of magnitude. These quantitative results have important implications for the effects of electrical coupling on the dynamic behavior of interneuron networks.

The minicolumn hypothesis in neuroscience

The minicolumn is a continuing source of research and debate more than half a century after it was identified as a component of brain organization. The minicolumn is a sophisticated local network that contains within it the elements for redundancy and plasticity. Although it is sometimes compared to subcortical nuclei, the design of the minicolumn is a distinctive form of module that has evolved specifically in the neocortex. It unites the horizontal and vertical components of cortex within the same cortical space. Minicolumns are often considered highly repetitive, even clone-like, units. However, they display considerable heterogeneity between areas and species, perhaps even within a given macrocolumn. Despite a growing recognition of the anatomical basis of the cortical minicolumn, as well as its physiological properties, the potential of the minicolumn has not been exploited in fields such as comparative neuroanatomy, abnormalities of the brain and mind, and evolution.