RESUMEN
The anatomy of the human piriform cortex (PC) is poorly understood. We used a bimodal connectivity-based-parcellation approach to investigate subregions of the PC and its connectional differentiation from the amygdala. One hundred (55 % female) genetically unrelated subjects from the Human Connectome Project were included. A region of interest (ROI) was delineated bilaterally covering PC and amygdala, and functional and structural connectivity of this ROI with the whole gray matter was computed. Spectral clustering was performed to obtain bilateral parcellations at granularities of k = 2-10 clusters and combined bimodal parcellations were computed. Validity of parcellations was assessed via their mean individual-to-group similarity per adjusted rand index (ARI). Individual-to-group similarity was higher than chance in both modalities and in all clustering solutions. The amygdala was clearly distinguished from PC in structural parcellations, and olfactory amygdala was connectionally more similar to amygdala than to PC. At higher granularities, an anterior and ventrotemporal and a posterior frontal cluster emerged within PC, as well as an additional temporal cluster at their boundary. Functional parcellations also showed a frontal piriform cluster, and similar temporal clusters were observed with less consistency. Results from bimodal parcellations were similar to the structural parcellations. Consistent results were obtained in a validation cohort. Distinction of the human PC from the amygdala, including its olfactory subregions, is possible based on its structural connectivity alone. The canonical fronto-temporal boundary within PC was reproduced in both modalities and with consistency. All obtained parcellations are freely available.
Asunto(s)
Amígdala del Cerebelo , Conectoma , Corteza Piriforme , Humanos , Femenino , Masculino , Corteza Piriforme/anatomía & histología , Corteza Piriforme/diagnóstico por imagen , Corteza Piriforme/fisiología , Adulto , Conectoma/métodos , Amígdala del Cerebelo/anatomía & histología , Amígdala del Cerebelo/diagnóstico por imagen , Imagen por Resonancia Magnética/métodos , Vías Nerviosas/anatomía & histología , Vías Nerviosas/diagnóstico por imagen , Adulto Joven , Red Nerviosa/diagnóstico por imagen , Red Nerviosa/anatomía & histologíaRESUMEN
The piriform cortex (paleocortex) is the olfactory cortex or the primary cortex for the sense of smell. It receives the olfactory input from the mitral and tufted cells of the olfactory bulb and is involved in the processing of information pertaining to odors. The piriform cortex and the adjoining neocortex have different cytoarchitectures; while the former has a three-layered structure, the latter has a six-layered structure. The regulatory mechanisms underlying the building of the six-layered neocortex are well established; in contrast, less is known about of the regulatory mechanisms responsible for structure formation of the piriform cortex. The differences as well as similarities in the regulatory mechanisms between the neocortex and the piriform cortex remain unclear. Here, the expression of neocortical layer-specific genes in the piriform cortex was examined. Two sublayers were found to be distinguished in layer II of the piriform cortex using Ctip2/Bcl11b and Brn1/Pou3f3. The sequential expression pattern of Ctip2 and Brn1 in the piriform cortex was similar to that detected in the neocortex, although the laminar arrangement in the piriform cortex exhibited an outside-in arrangement, unlike that observed in the neocortex.
Asunto(s)
Neocórtex/anatomía & histología , Corteza Piriforme/anatomía & histología , Animales , Ratones , Neocórtex/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuronas/metabolismo , Factores del Dominio POU/metabolismo , Corteza Piriforme/metabolismo , Proteínas Represoras/metabolismo , Factores de Tiempo , Proteínas Supresoras de Tumor/metabolismoRESUMEN
The piriform cortex is a distinct brain region that plays a key role in the sense of smell. The piriform cortex is the major part of primary olfactory cortex and has broad connections that extend beyond the olfactory regions into limbic and fronto-temporal cortical networks. Numerous studies have described these anatomical connections via microscopic imaging and tracer studies. More recently, macroscopic anatomical imaging studies have demonstrated changes in the piriform cortex in humans with focal epilepsy as well as in animal models, suggesting this brain region can play a critical role in epileptogenesis. This review examines the imaging methods and techniques that have been most informative, leading to our current understanding of the anatomy and subdivsions of the piriform cortex as well as its connections to other brain structures, and the abnormalities that can be detected in the setting of epilepsy.
Asunto(s)
Neuroimagen/métodos , Corteza Piriforme/anatomía & histología , Animales , Epilepsia/diagnóstico por imagen , Humanos , Corteza Piriforme/diagnóstico por imagenRESUMEN
Sensory processing is strongly modulated by different brain and behavioral states, and this is based on the top-down modulation. In the olfactory system, local neural circuits in the olfactory bulb (OB) are innervated by centrifugal afferents in order to regulate the processing of olfactory information in the OB under different behavioral states. The purpose of the present study was to explore the organization of neural networks in olfactory-related cortices and modulatory nuclei that give rise to direct and indirect innervations to the glomerular layer (GL) of the OB at the whole-brain scale. Injection of different recombinant attenuated neurotropic viruses into the GL showed that it received direct inputs from each layer in the OB, centrifugal inputs from the ipsilateralanterior olfactory nucleus (AON), anterior piriform cortex (Pir), and horizontal limb of diagonal band of Broca (HDB), and various indirect inputs from bilateral cortical neurons in the AON, Pir, amygdala, entorhinal cortex, hippocampus, HDB, dorsal raphe, median raphe and locus coeruleus. These results provide a circuitry basis that will help further understand the mechanism by which olfactory information-processing in the OB is regulated.
Asunto(s)
Vías Aferentes/anatomía & histología , Bulbo Olfatorio/anatomía & histología , Vías Olfatorias/anatomía & histología , Amígdala del Cerebelo/anatomía & histología , Animales , Encéfalo/anatomía & histología , Banda Diagonal de Broca/anatomía & histología , Hipocampo/anatomía & histología , Masculino , Ratones , Ratones Endogámicos C57BL , Corteza Piriforme/anatomía & histologíaRESUMEN
The underlying mechanisms responsible for enhanced olfactory perception of congenital blind humans remain elusive so far. Here, animal behavioral test showed that congenital visual deprivation (from postnatal day 0-28) or one-week visual deprivation during juvenile stage (from postnatal day 21-28) could reduce the latency time of food-seeking but increase the odor discrimination performance of rodents. The enhanced olfactory perception induced by one-week visual deprivation could be returned to base level when visual input was recovered. Accordingly, local field potential (LFP) oscillation recording in vivo showed that the power of high-frequency ß and γ oscillations were increased in olfactory bulb (OB) and anterior piriform cortex (aPC) of vision deprived animals. This research discovered the enhancement of olfactory perception and adaptive plasticity of oscillations in olfactory system of rodents induced by visual deprivation, which may facilitate better understanding of mechanisms underlying cross-modal plasticity.
Asunto(s)
Potenciales Evocados Somatosensoriales/fisiología , Plasticidad Neuronal/fisiología , Vías Olfatorias/fisiología , Percepción Olfatoria/fisiología , Privación Sensorial , Animales , Animales Recién Nacidos , Oscuridad , Ratones , Ratones Endogámicos C57BL , Odorantes/análisis , Bulbo Olfatorio/anatomía & histología , Bulbo Olfatorio/fisiología , Corteza Piriforme/anatomía & histología , Corteza Piriforme/fisiología , Ratas , Ratas Sprague-Dawley , Visión Ocular/fisiologíaRESUMEN
Neurons in the neocortex exhibit spontaneous spiking activity in the absence of external stimuli, but the origin and functions of this activity remain uncertain. Here, we show that spontaneous spiking is also prominent in a sensory paleocortex, the primary olfactory (piriform) cortex of mice. In the absence of applied odors, piriform neurons exhibit spontaneous firing at mean rates that vary systematically among neuronal classes. This activity requires the participation of NMDA receptors and is entirely driven by bottom-up spontaneous input from the olfactory bulb. Odor stimulation produces two types of spatially dispersed, odor-distinctive patterns of responses in piriform cortex layer 2 principal cells: Approximately 15% of cells are excited by odor, and another approximately 15% have their spontaneous activity suppressed. Our results show that, by allowing odor-evoked suppression as well as excitation, the responsiveness of piriform neurons is at least twofold less sparse than currently believed. Hence, by enabling bidirectional changes in spiking around an elevated baseline, spontaneous activity in the piriform cortex extends the dynamic range of odor representation and enriches the coding space for the representation of complex olfactory stimuli.
Asunto(s)
Potenciales de Acción/fisiología , Odorantes/análisis , Vías Olfatorias/fisiología , Percepción Olfatoria/fisiología , Corteza Piriforme/fisiología , Células Receptoras Sensoriales/metabolismo , Olfato/fisiología , Animales , Femenino , Expresión Génica , Masculino , Ratones , Ratones Endogámicos C57BL , Bulbo Olfatorio/anatomía & histología , Bulbo Olfatorio/citología , Bulbo Olfatorio/fisiología , Vías Olfatorias/anatomía & histología , Técnicas de Placa-Clamp , Corteza Piriforme/anatomía & histología , Corteza Piriforme/citología , Receptores de N-Metil-D-Aspartato/genética , Receptores de N-Metil-D-Aspartato/metabolismo , Células Receptoras Sensoriales/clasificación , Células Receptoras Sensoriales/citología , Técnicas EstereotáxicasRESUMEN
The neocortex is found only in mammals, and the fossil record is silent on how this soft tissue evolved. Understanding neocortex evolution thus devolves to a search for candidate homologous neocortex traits in the extant nonmammalian amniotes. The difficulty is that homology is based on similarity, and the six-layered neocortex structure could hardly be more dissimilar in appearance from the nuclear organization that is so conspicuous in the dorsal telencephalon of birds and other reptiles. Recent molecular data have, however, provided new support for one prominent hypothesis, based on neuronal circuits, that proposes the principal neocortical input and output cell types are a conserved feature of amniote dorsal telencephalon. Many puzzles remain, the greatest being understanding the selective pressures and molecular mechanisms that underlie such tremendous morphological variation in telencephalon structure.
Asunto(s)
Neocórtex/anatomía & histología , Corteza Piriforme/anatomía & histología , Animales , Evolución Biológica , Aves/anatomía & histología , Mamíferos/anatomía & histología , Reptiles/anatomía & histologíaRESUMEN
The piriform cortex (PCX) is the largest component of the olfactory cortex and is hypothesized to be the locus of odor object formation. The distributed odorant representation found in PCX contrasts sharply with the topographical representation seen in other primary sensory cortices, making it difficult to test this view. Recent work in PCX has focused on functional characteristics of these distributed afferent and association fiber systems. However, information regarding the efferent projections of PCX and how those may be involved in odor representation and object recognition has been largely ignored. To investigate this aspect of PCX, we have used the efferent pathway from mouse PCX to the orbitofrontal cortex (OFC). Using double fluorescent retrograde tracing, we identified the output neurons (OPNs) of the PCX that project to two subdivisions of the OFC, the agranular insula and the lateral orbitofrontal cortex (AI-OPNs and LO-OPNs, respectively). We found that both AI-OPNs and LO-OPNs showed a distinct spatial topography within the PCX and fewer than 10% projected to both the AI and the LO as judged by double-labeling. These data revealed that the efferent component of the PCX may be topographically organized. Further, these data suggest a model for functional organization of the PCX in which the OPNs are grouped into parallel output circuits that provide olfactory information to different higher centers. The distributed afferent input from the olfactory bulb and the local PCX association circuits would then ensure a complete olfactory representation, pattern recognition capability, and neuroplasticity in each efferent circuit.