Cortical neurons projecting to the posterior part of the superior temporal sulcus with particular reference to the posterior association area. An HRP study in the monkey

Corticocortical connections from the posterior association area to the posterior part of the superior temporal sulcal cortex (STs area) were studied in the monkey by means of retrograde axonal transport of horseradish peroxidase (HRP) or wheatgerm-agglutinin-conjugated HRP (WGA-HRP). After injecting 0.05-0.2 microliter of 50% HRP or 5% WGA-HRP into the STs area, labeled cells were examined in various cortical regions. The dorsal wall of the STs receives fibers mainly from the inferior parietal lobule (area 7) and superior temporal gyrus (area 22), whereas the ventral wall and floor part of the STs receive fibers from the posterior inferotemporal gyrus (area TEO) and prestriate cortex (areas 18 and 19). The deeper parts of the dorsal wall close to the floor region of the STs area also receive many fibers from the cortical walls surrounding the intraparietal, lunate and lateral sulci. Both the dorsal and ventral cortical walls of the intraparietal sulcus send fibers mainly to the deep dorsal wall of the STs. The ventral wall of the STs, on the other hand, receives fibers only from the ventral wall of the intraparietal sulcus. The medial surface of the prestriate cortex and the parahippocampal region send fibers to both walls of the STs. In the prestriate-STs projections originating from areas around the parieto-occipital sulcus, a topographic correlation is present; area 19 located anterior to the sulcus projects to the dorsal wall, whereas area 18 situated posterior to the sulcus projects to the ventral wall. Only the dorsal wall receives fibers from the cingulate (areas 23 and 24) and subparietal gyri (area 7). The deeper part of the dorsal wall and the ventral wall of the posterior STs area are interconnected with each other, while the upper part of the dorsal wall does not appear to receive fibers from the ventral wall.     

Functional and structural alterations of the intraparietal sulcus in a developmental dyscalculia of genetic origin

Cognitive theories of numerical representation suggest that understanding of numerical quantities is driven by a magnitude representation associated with the intraparietal sulcus and possibly under genetic control. The aim of this study was to investigate, using fMRI and structural imaging, the interaction between the abnormal development of numerical representation in an X-linked condition, Turner syndrome (TS), and the development of the intraparietal sulcus. fMRI during exact and approximate calculation in TS showed an abnormal modulation of intraparietal activations as a function of number size. Morphological analysis revealed an abnormal length, depth, and sulcal geometry of the right intraparietal sulcus, suggesting an important disorganization of this region in TS. Thus, a genetic form of developmental dyscalculia can be related to both functional and structural anomalies of the right intraparietal sulcus, suggesting a crucial role of this region in the development of arithmetic abilities.     

Cortico-cortical projections from the prefrontal cortex to the superior temporal sulcal area (STs) in the monkey studied by means of HRP method.

Cortico-cortical connections from the prefrontal cortex to the superior temporal sulcal cortex (STs area) were studied in the monkey by means of retrograde axonal transport of horseradish peroxidase (HRP). After injections of 0.15-0.6 microliter of 50% HRP into the STs area, labeled cells were found in various cortical regions. In the prefrontal-STs projections, main features of topographic correlation were revealed; the posterior part of the STs area receives fibers from the superior frontal convexity (areas dorsal to the principal sulcus) and areas 8 and 6, whereas the anterior part of the STs area receives fibers from the inferior frontal convexity (areas ventral to the principal sulcus) and the frontal pole (area FD). The principal sulcus sends fibers to the entire STs area except for its ventral wall of the posterior part. A small cortical area adjacent to the inferior ramus of the arcuate sulcus (area 45 of ref. 41) sends fibers to the entire STs area. In addition, the orbitofrontal cortex projects mainly to the rostral part of the STs area, and the parahippocampal gyrus (areas TF and TH) projects to the deeper part of the entire STs area.     

Neural representation of auditory size in the human voice and in sounds from other resonant sources

The size of a resonant source can be estimated by the acoustic-scale information in the sound [1-3]. Previous studies revealed that posterior superior temporal gyrus (STG) responds to acoustic scale in human speech when it is controlled for spectral-envelope change (unpublished data). Here we investigate whether the STG activity is specific to the processing of acoustic scale in human voice or whether it reflects a generic mechanism for the analysis of acoustic scale in resonant sources. In two functional magnetic resonance imaging (fMRI) experiments, we measured brain activity in response to changes in acoustic scale in different categories of resonant sound (human voice, animal call, and musical instrument). We show that STG is activated bilaterally for spectral-envelope changes in general; it responds to changes in category as well as acoustic scale. Activity in left posterior STG is specific to acoustic scale in human voices and not responsive to acoustic scale in other resonant sources. In contrast, the anterior temporal lobe and intraparietal sulcus are activated by changes in acoustic scale across categories. The results imply that the human voice requires special processing of acoustic scale, whereas the anterior temporal lobe and intraparietal sulcus process auditory size information independent of source category.     

Crossmodal processing of object features in human anterior intraparietal cortex: an fMRI study implies equivalencies between humans and monkeys

The organization of macaque posterior parietal cortex (PPC) reflects its functional specialization in integrating polymodal sensory information for object recognition and manipulation. Neuropsychological and recent human imaging studies imply equivalencies between human and macaque PPC, and in particular, the cortex buried in the intraparietal sulcus (IPS). Using functional MRI, we tested the hypothesis that an area in human anterior intraparietal cortex is activated when healthy subjects perform a crossmodal visuo-tactile delayed matching-to-sample task with objects. Tactile or visual object presentation (encoding and recognition) both significantly activated anterior intraparietal cortex. As hypothesized, neural activity in this area was further enhanced when subjects transferred object information between modalities (crossmodal matching). Based on both the observed functional properties and the anatomical location, we suggest that this area in anterior IPS is the human equivalent of macaque area AIP.     

Maps of space in human frontoparietal cortex

Prefrontal cortex (PFC) and posterior parietal cortex (PPC) are neural substrates for spatial cognition. We here review studies in which we tested the hypothesis that human frontoparietal cortex may function as a priority map. According to priority map theory, objects or locations in the visual world are represented by neural activity that is proportional to their attentional priority. Using functional magnetic resonance imaging (fMRI), we first identified topographic maps in PFC and PPC as candidate priority maps of space. We then measured fMRI activity in candidate priority maps during the delay periods of a covert attention task, a spatial working memory task, and a motor planning task to test whether the activity depended on the particular spatial cognition. Our hypothesis was that some, but not all, candidate priority maps in PFC and PPC would be agnostic with regard to what was being prioritized, in that their activity would reflect the location in space across tasks rather than a particular kind of spatial cognition (e.g., covert attention). To test whether patterns of delay period activity were interchangeable during the spatial cognitive tasks, we used multivariate classifiers. We found that decoders trained to predict the locations on one task (e.g., working memory) cross-predicted the locations on the other tasks (e.g., covert attention and motor planning) in superior precentral sulcus (sPCS) and in a region of intraparietal sulcus (IPS2), suggesting that these patterns of maintenance activity may be interchangeable across the tasks. Such properties make sPCS in frontal cortex and IPS2 in parietal cortex viable priority map candidates, and suggest that these areas may be the human homologs of the monkey frontal eye field (FEF) and lateral intraparietal area (LIP).     

Uncovering the spatio-temporal dynamics of value-based decision-making in the human brain: a combined fMRI–EEG study

While there is a growing body of functional magnetic resonance imaging (fMRI) evidence implicating a corpus of brain regions in value-based decision-making in humans, the limited temporal resolution of fMRI cannot address the relative temporal precedence of different brain regions in decision-making. To address this question, we adopted a computational model-based approach to electroencephalography (EEG) data acquired during a simple binary choice task. fMRI data were also acquired from the same participants for source localization. Post-decision value signals emerged 200 ms post-stimulus in a predominantly posterior source in the vicinity of the intraparietal sulcus and posterior temporal lobe cortex, alongside a weaker anterior locus. The signal then shifted to a predominantly anterior locus 850 ms following the trial onset, localized to the ventromedial prefrontal cortex and lateral prefrontal cortex. Comparison signals between unchosen and chosen options emerged late in the trial at 1050 ms in dorsomedial prefrontal cortex, suggesting that such comparison signals may not be directly associated with the decision itself but rather may play a role in post-decision action selection. Taken together, these results provide us new insights into the temporal dynamics of decision-making in the brain, suggesting that for a simple binary choice task, decisions may be encoded predominantly in posterior areas such as intraparietal sulcus, before shifting anteriorly.     

Anatomical evidence for the posterior boundary of area 2 in the macaque monkey

This study examined the architectonic organization of the macaque's primary somatosensory cortex near the tip of the intraparietal sulcus (IPS), using myelin and Nissl stains plus immunohistochemical labeling with the SMI-32 antibody. The surface cortex between the IPS and central sulcus (overlapping area 2) was distinguished from surrounding cortex (areas 1 and 5) by relatively light SMI-32 immunoreactivity. This distinguishing architectonic feature was most evident between the post-central dimple and cortex immediately anterior to the tip of the IPS. Physiological mappings verified that the architectonic transition correlated with a change in receptive field properties, consistent with their marking the boundary between areas 2 and 5. These results suggest that area 2 occupies surface cortex anterior to the IPS, but not within the IPS.     

Anatomical evidence for the posterior boundary of area 2 in the macaque monkey

This study examined the architectonic organization of the macaque's primary somatosensory cortex near the tip of the intraparietal sulcus (IPS), using myelin and Nissl stains plus immunohistochemical labeling with the SMI-32 antibody. The surface cortex between the IPS and central sulcus (overlapping area 2) was distinguished from surrounding cortex (areas 1 post-central dimple and cortex immediately anterior to the tip of the IPS. Physiological mappings verified that the and 5) by relatively light SMI-32 immunoreactivity. This distinguishing architectonic feature was most evident between the architectonic transition correlated with a change in receptive field properties, consistent with their marking the boundary between areas 2 and 5. These results suggest that area 2 occupies surface cortex anterior to the IPS, but not within the IPS.     

Distinct Parietal and Temporal Pathways to the Homologues of Broca's Area in the Monkey

The homologues of the two distinct architectonic areas 44 and 45 that constitute the anterior language zone (Broca's region) in the human ventrolateral frontal lobe were recently established in the macaque monkey. Although we know that the inferior parietal lobule and the lateral temporal cortical region project to the ventrolateral frontal cortex, we do not know which of the several cortical areas found in those regions project to the homologues of Broca's region in the macaque monkey and by means of which white matter pathways. We have used the autoradiographic method, which permits the establishment of the cortical area from which axons originate (i.e., the site of injection), the precise course of the axons in the white matter, and their termination within particular cortical areas, to examine the parietal and temporal connections to area 44 and the two subdivisions of area 45 (i.e., areas 45A and 45B). The results demonstrated a ventral temporo-frontal stream of fibers that originate from various auditory, multisensory, and visual association cortical areas in the intermediate superolateral temporal region. These axons course via the extreme capsule and target most strongly area 45 with a more modest termination in area 44. By contrast, a dorsal stream of axons that originate from various cortical areas in the inferior parietal lobule and the adjacent caudal superior temporal sulcus was found to target both areas 44 and 45. These axons course in the superior longitudinal fasciculus, with some axons originating from the ventral inferior parietal lobule and the adjacent superior temporal sulcus arching and forming a simple arcuate fasciculus. The cortex of the most rostral part of the inferior parietal lobule is preferentially linked with the ventral premotor cortex (ventral area 6) that controls the orofacial musculature. The cortex of the intermediate part of the inferior parietal lobule is linked with both areas 44 and 45. These findings demonstrate the posterior parietal and temporal connections of the ventrolateral frontal areas, which, in the left hemisphere of the human brain, were adapted for various aspects of language production. These precursor circuits that are found in the nonlinguistic, nonhuman, primate brain also exist in the human brain. The possible reasons why these areas were adapted for language use in the human brain are discussed. The results throw new light on the prelinguistic precursor circuitry of Broca's region and help understand functional interactions between Broca's ventrolateral frontal region and posterior parietal and temporal association areas.     

Effective Connectivity of Depth-Structure–Selective Patches in the Lateral Bank of the Macaque Intraparietal Sulcus

Extrastriate cortical areas are frequently composed of subpopulations of neurons encoding specific features or stimuli, such as color, disparity, or faces, and patches of neurons encoding similar stimulus properties are typically embedded in interconnected networks, such as the attention or face-processing network. The goal of the current study was to examine the effective connectivity of subsectors of neurons in the same cortical area with highly similar neuronal response properties. We first recorded single- and multi-unit activity to identify two neuronal patches in the anterior part of the macaque intraparietal sulcus (IPS) showing the same depth structure selectivity and then employed electrical microstimulation during functional magnetic resonance imaging in these patches to determine the effective connectivity of these patches. The two IPS subsectors we identified—with the same neuronal response properties and in some cases separated by only 3 mm—were effectively connected to remarkably distinct cortical networks in both dorsal and ventral stream in three macaques. Conversely, the differences in effective connectivity could account for the known visual-to-motor gradient within the anterior IPS. These results clarify the role of the anterior IPS as a pivotal brain region where dorsal and ventral visual stream interact during object analysis. Thus, in addition to the anatomical connectivity of cortical areas and the properties of individual neurons in these areas, the effective connectivity provides novel key insights into the widespread functional networks that support behavior.     

Uniquely human social cognition

Recent data identify distinct components of social cognition associated with five brain regions. In posterior temporal cortex, the extrastriate body area is associated with perceiving the form of other human bodies. A nearby region in the posterior superior temporal sulcus is involved in interpreting the motions of a human body in terms of goals. A distinct region at the temporo-parietal junction supports the uniquely human ability to reason about the contents of mental states. Medial prefrontal cortex is divided into at least two subregions. Ventral medial prefrontal cortex is implicated in emotional empathy, whereas dorsal medial prefrontal cortex is implicated in the uniquely human representation of triadic relations between two minds and an object, supporting shared attention and collaborative goals.     

Projections from the cortex of the superior temporal sulcus to the dorsal lateral geniculate and pregeniculate nuclei in the macaque monkey

Cortical projections from the visual region and adjacent polysensory region of the superior temporal sulcus (STs) to the lateral geniculate body (LGb) were investigated in the macaque monkey using an autoradiographic tracing method. Solutions of tritiated aminoacids were injected into different parts of the caudal half of the STs of five animals. A survival time of 7 days was allowed. Labels were found in both subdivisions of the LGb: the dorsal lateral geniculate nucleus (DLGn) and the pregeniculate nucleus (PGn). In particular, part of the visual cortical region adjacent to the middle temporal area (MT) projects into the DLGn as well as the PGn, whereas the MT itself and the superior temporal polysensory region project into the PGn only. Afferents to the DLGn terminate in the magnocellular layers and in their adjoining interlaminar zones, completely sparing the parvocellular layers. Afferents to the PGn terminate in separate regions of this nucleus; the MT and adjacent visual cortices project into the internal layer of the PGn, whereas the polysensosy region of the STs projects into the external retinorecipient layer of the PGn. Possible functional implications of these projections are discussed.     

川金丝猴脑的动脉供应

为了探讨川金丝猴脑动脉供应的形态学特征,为脑生物学研究提供结构基础,用血管铸型和组织透明方法追踪观察了川金丝猴幼体脑动脉的来源和分支分布。结果表明川金丝猴与人脑的动脉供应基本相同,也由颈内动脉和椎动脉供应。上述动脉的分支于垂体周围形成大脑动脉环。颈内动脉通过大脑前动脉和大脑中动脉主要供应大脑半球前部的血液,椎动脉参与形成基底动脉、小脑动脉系和大脑后动脉,供应脑干、小脑和大脑后部的血液。另外,川金丝猴幼体左、右大脑前动脉间缺少前交通动脉。     

The Vascularization of the Anuran Brain: The Mesencephalon

The angioarchitecture of the toad's mesencephalon is studied by scanning electron microscopy of vascular corrosion casts. The arterial supply is performed by the superior mesencephalic artery and by an artery arising from the ramus posterior of the arteria carotis cerebralis just in front of the retroin-fundibular communicating artery. The venous drainage is exerted by the vena diencephalica, the vena lateralis mesencephalis and by anterior and posterior branches of the encephaloposthypophysial portal vein. Characteristics of the mesencephalic angioarchitecture are the centrifugal direction of the blood flow, the intensive capillarization, and the formation of vascular meshworks in the region of the stratum griseum periventriculare tecti and of the stratum griseum superficiale tecti.     

The number domain- can we count on parietal cortex?

Does the primate brain contain a dedicated and localized neural circuitry for processing generic numerical information? The human parietal cortex, particularly the intraparietal sulcus (IPS), has long been implicated in processing symbolic (verbal) number information. If the IPS is indeed the site of generic numerical processing, however, its neurons should also encode nonsymbolic numerosity information. Two recent studies by Shuman and Kanwisher and by Piazza et al. published in this issue of Neuron tested this assumption...with quite different results.     

Spatio-Temporal Dynamics of Human Intention Understanding in Temporo-Parietal Cortex: A Combined EEG/fMRI Repetition Suppression Paradigm

Inferring the intentions of other people from their actions recruits an inferior fronto-parietal action observation network as well as a putative social network that includes the posterior superior temporal sulcus (STS). However, the functional dynamics within and among these networks remains unclear. Here we used functional magnetic resonance imaging (fMRI) and high-density electroencephalogram (EEG), with a repetition suppression design, to assess the spatio-temporal dynamics of decoding intentions. Suppression of fMRI activity to the repetition of the same intention was observed in inferior frontal lobe, anterior intraparietal sulcus (aIPS), and right STS. EEG global field power was reduced with repeated intentions at an early (starting at 60 ms) and a later (∼330 ms) period after the onset of a hand-on-object encounter. Source localization during these two intervals involved right STS and aIPS regions highly consistent with RS effects observed with fMRI. These results reveal the dynamic involvement of temporal and parietal networks at multiple stages during the intention decoding and without a strict segregation of intention decoding between these networks.     

Multimodal spatial representations engaged in human parietal cortex during both saccadic and manual spatial orienting

BACKGROUND: Recent neuroimaging studies have found that several areas of the human brain, including parietal regions, can respond multimodally. But given single-cell evidence that responses in primate parietal cortex can be motor-related, some of the human multimodal activations might reflect convergent activation of potentially motor-related areas, rather than multimodal representations of space independent of motor factors. Here we crossed sensory stimulation of different modalities (vision or touch, in left or right hemifield) with spatially directed responses to such stimulation by different effector-systems (saccadic or manual). RESULTS: The fMRI results revealed representations of contralateral space in both the posterior part of the superior parietal gyrus and the anterior intraparietal sulcus that activated independently of both sensory modality and motor response. Multimodal saccade-related or manual-related activations were found, by contrast, in different regions of parietal cortex. CONCLUSIONS: Whereas some parietal regions have specific motor functions, others are engaged during the execution of movements to the contralateral hemifield irrespective of both input modality and the type of motor effector.     

Cortical gyrification and sulcal spans in early stage Alzheimer's disease

Alzheimer's disease (AD) is characterized by an insidious onset of progressive cerebral atrophy and cognitive decline. Previous research suggests that cortical folding and sulcal width are associated with cognitive function in elderly individuals, and the aim of the present study was to investigate these morphological measures in patients with AD. The sample contained 161 participants, comprising 80 normal controls, 57 patients with very mild AD, and 24 patients with mild AD. From 3D T1-weighted brain scans, automated methods were used to calculate an index of global cortex gyrification and the width of five individual sulci: superior frontal, intra-parietal, superior temporal, central, and Sylvian fissure. We found that global cortex gyrification decreased with increasing severity of AD, and that the width of all individual sulci investigated other than the intra-parietal sulcus was greater in patients with mild AD than in controls. We also found that cognitive functioning, as assessed by Mini-Mental State Examination (MMSE) scores, decreased as global cortex gyrification decreased. MMSE scores also decreased in association with a widening of all individual sulci investigated other than the intra-parietal sulcus. The results suggest that abnormalities of global cortex gyrification and regional sulcal span are characteristic of patients with even very mild AD, and could thus facilitate the early diagnosis of this condition.     

Separate coding of different gaze directions in the superior temporal sulcus and inferior parietal lobule

Electrophysiological recording in the anterior superior temporal sulcus (STS) of monkeys has demonstrated separate cell populations responsive to direct and averted gaze. Human functional imaging has demonstrated posterior STS activation in gaze processing, particularly in coding the intentions conveyed by gaze, but to date has provided no evidence of dissociable coding of different gaze directions. Because the spatial resolution typical of group-based fMRI studies (approximately 6-10 mm) exceeds the size of cellular patches sensitive to different facial characteristics (1-4 mm in monkeys), a more sensitive technique may be required. We therefore used fMRI adaptation, which is considered to offer superior resolution, to investigate whether the human anterior STS contains representations of different gaze directions, as suggested by non-human primate research. Subjects viewed probe faces gazing left, directly ahead, or right. Adapting to leftward gaze produced a reduction in BOLD response to left relative to right (and direct) gaze probes in the anterior STS and inferior parietal cortex; rightward gaze adaptation produced a corresponding reduction to right gaze probes. Consistent with these findings, averted gaze in the adapted direction was misidentified as direct. Our study provides the first human evidence of dissociable neural systems for left and right gaze.