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Population Coding of Visual Space: Comparison of Spatial Representations in Dorsal and Ventral Pathways  [PDF]
Anne B. Sereno,Sidney R. Lehky
Frontiers in Computational Neuroscience , 2011, DOI: 10.3389/fncom.2010.00159
Abstract: Although the representation of space is as fundamental to visual processing as the representation of shape, it has received relatively little attention from neurophysiological investigations. In this study we characterize representations of space within visual cortex, and examine how they differ in a first direct comparison between dorsal and ventral subdivisions of the visual pathways. Neural activities were recorded in anterior inferotemporal cortex (AIT) and lateral intraparietal cortex (LIP) of awake behaving monkeys, structures associated with the ventral and dorsal visual pathways respectively, as a stimulus was presented at different locations within the visual field. In spatially selective cells, we find greater modulation of cell responses in LIP with changes in stimulus position. Further, using a novel population-based statistical approach (namely, multidimensional scaling), we recover the spatial map implicit within activities of neural populations, allowing us to quantitatively compare the geometry of neural space with physical space. We show that a population of spatially selective LIP neurons, despite having large receptive fields, is able to almost perfectly reconstruct stimulus locations within a low-dimensional representation. In contrast, a population of AIT neurons, despite each cell being spatially selective, provide less accurate low-dimensional reconstructions of stimulus locations. They produce instead only a topologically (categorically) correct rendition of space, which nevertheless might be critical for object and scene recognition. Furthermore, we found that the spatial representation recovered from population activity shows greater translation invariance in LIP than in AIT. We suggest that LIP spatial representations may be dimensionally isomorphic with 3D physical space, while in AIT spatial representations may reflect a more categorical representation of space (e.g., “next to” or “above”).
Dorsal Versus Ventral Oral Mucosal Graft Urethroplasty
Jalil Hosseini,Ali Kaviani,Mokhtar Hosseini,,Mohammad Mohsen Mazloomfard
Urology Journal , 2011,
Abstract: PURPOSE: To evaluate success rate of dorsal versus ventral oral mucosal graft for anterior urethroplasty.MATERIALS AND METHODS: In a retrospective study, the results of the ventral and dorsal oral mucosal graft (OMG) anterior urethroplasty were assessed in 24 and 29 patients, respectively. Demographic and clinical characteristics of subjects were gathered from the medical records.RESULTS: Patients were followed up for a mean duration of 32 months (range, 25 to 51 months). The success rates of dorsal and ventral anterior OMG urethroplasty were 83.3% and 75.8%, respectively (P = .5). At penile site, dorsal and ventral OMG were done for 9 and 10 patients with stricture lengths of 3.7 ± 1.1 cm and 3.9 ± 1.2 cm, respectively (P = .7). Success rates of dorsal and ventral penile OMG were 88.9% and 70%, respectively (P = .3). At the bulbar site, dorsal and ventral OMG were performed on 15 and 19 patients with stricture lengths of 4.1 ± 1.1cm and 4.2 ± 1.5 cm, respectively (P = .7). The success rates of dorsal and ventral bulbar OMG were 80% and 79%, respectively (P = .94).CONCLUSION: Oral mucosal graft is a versatile and an effective procedure for management of strictures throughout the anterior urethra, and in experienced hands, the outcomes are similarly favorable whether a dorsal or ventral approach is taken.
Ventral and dorsal streams in the evolution of speech and language  [PDF]
Josef P. Rauschecker
Frontiers in Evolutionary Neuroscience , 2012, DOI: 10.3389/fnevo.2012.00007
Abstract: The brains of humans and old-world monkeys show a great deal of anatomical similarity. The auditory cortical system, for instance, is organized into a ventral and a dorsal pathway in both species. A fundamental question with regard to the evolution of speech and language (as well as music) is whether human and monkey brains show principal differences in their organization (e.g., new pathways appearing as a result of a single mutation), or whether species differences are of a more subtle, quantitative nature. There is little doubt about a similar role of the ventral auditory pathway in both humans and monkeys in the decoding of spectrally complex sounds, which some authors have referred to as auditory object recognition. This includes the decoding of speech sounds (“speech perception”) and their ultimate linking to meaning in humans. The originally presumed role of the auditory dorsal pathway in spatial processing, by analogy to the visual dorsal pathway, has recently been conceptualized into a more general role in sensorimotor integration and control. Specifically for speech, the dorsal processing stream plays a role in speech production as well as categorization of phonemes during on-line processing of speech.
G. R. Hassanzadeh G. Behzadi
Acta Medica Iranica , 2007,
Abstract: The ascending serotonergic projections are derived mainly from mesencephalic raphe nuclei. Topographical projections from mesencephalic raphe nuclei to the striatum were examined in the rat by the retrograde transport technique of HRP (horseradish peroxidase). In 29 rats stereotaxically injection of HRP enzyme were performed in dorsal and ventral parts of striatum separately. The extent of the injection sites and distribution of retrogradely labeled neuronal cell bodies were drawed on representative sections using a projection microscope. Following ipsilateral injection of HRP into the dorsal striatum, numerous labeled neurons were seen in rostral portion of dorsal raphe (DR) nucleus. In the same level the cluster of labeled neurons were hevier through caudal parts of DR. A few neurons were also located in lateral wing of DR. More caudally some labeled neurons were found in lateral, medial line of DR. In median raphe nucleus (MnR) the labeled neurons were scattered only in median portion of this nucleus. The ipsilateral injection of HRP into the ventral region of striatum resulted on labeling of numerous neurons in rostral, caudal and lateral portions of DR. Through the caudal extension of DR on 4th ventricle level, a large number of labeled neurons were distributed along the ventrocaudal parts of DR. In MnR, labeled neurons were observed only in median part of this nucleus. These findings suggest the mesencephalic raphe nuclei projections to caudo-putamen are topographically organized. In addition dorsal and median raphe nuclei have a stronger projection to the ventral striatum.
Disturbed Resting Functional Inter-Hemispherical Connectivity of the Ventral Attentional Network in Alpha Band Is Associated with Unilateral Spatial Neglect  [PDF]
Tsutomu Sasaki, Masayuki Abe, Eiichi Okumura, Toyoji Okada, Kimito Kondo, Kensuke Sekihara, Wataru Ide, Hajime Kamada
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0073416
Abstract: Unilateral spatial neglect (USN) is one of the most common symptoms of right hemisphere damage; its classical symptom is that patients fail to respond to information on their left side. It has been postulated that disturbance of 2 separate attentional networks relates to the occurrence of USN. However, little is known about the underlying mechanism and neuronal substrates. In this study, we measured spontaneous neural activity by means of magnetoencephalography in 13 patients with brain damage and 5 control subjects. To study the relationship between functional connectivity at rest and severity of USN symptoms, we determined the imaginary coherence values relating to the inter-hemispherical ventral and dorsal attentional networks, as well as the clinical severity of USN using neuropsychological tests and behavioral rating scales. The present results showed that inter-hemispherical connectivity in the ventral attentional network, especially between the left and right angular gyri, detected in the alpha band is associated with the severity of USN symptoms. This may suggest that connectivity of inter-hemispherical homologous regions of the ventral attentional network in the alpha band could be one of the biomarkers of attentional network imbalance occurring in patients with USN.
Top-Down Modulations from Dorsal Stream in Lexical Recognition: An Effective Connectivity fMRI Study  [PDF]
Yuan Deng, Ruifang Guo, Guosheng Ding, Danling Peng
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0033337
Abstract: Both the ventral and dorsal visual streams in the human brain are known to be involved in reading. However, the interaction of these two pathways and their responses to different cognitive demands remains unclear. In this study, activation of neural pathways during Chinese character reading was acquired by using a functional magnetic resonance imaging (fMRI) technique. Visual-spatial analysis (mediated by the dorsal pathway) was disassociated from lexical recognition (mediated by the ventral pathway) via a spatial-based lexical decision task and effective connectivity analysis. Connectivity results revealed that, during spatial processing, the left superior parietal lobule (SPL) positively modulated the left fusiform gyrus (FG), while during lexical processing, the left SPL received positive modulatory input from the left inferior frontal gyrus (IFG) and sent negative modulatory output to the left FG. These findings suggest that the dorsal stream is highly involved in lexical recognition and acts as a top-down modulator for lexical processing.
Dissociation between Dorsal and Ventral Posterior Parietal Cortical Responses to Incidental Changes in Natural Scenes  [PDF]
Lorelei R. Howard, Dharshan Kumaran, H. Freyja ólafsdóttir, Hugo J. Spiers
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0067988
Abstract: Background The posterior parietal cortex (PPC) is thought to interact with the medial temporal lobe (MTL) to support spatial cognition and topographical memory. While the response of medial temporal lobe regions to topographical stimuli has been intensively studied, much less research has focused on the role of PPC and its functional connectivity with the medial temporal lobe. Methodology/Principle Findings Here we report a dissociation between dorsal and ventral regions of PPC in response to different types of change in natural scenes using an fMRI adaptation paradigm. During scanning subjects performed an incidental target detection task whilst viewing trial unique sequentially presented pairs of natural scenes, each containing a single prominent object. We observed a dissociation between the superior parietal gyrus and the angular gyrus, with the former showing greater sensitivity to spatial change, and the latter showing greater sensitivity to scene novelty. In addition, we observed that the parahippocampal cortex has increased functional connectivity with the angular gyrus, but not superior parietal gyrus, when subjects view change to the scene content. Conclusions/Significance Our findings provide support for proposed dissociations between dorsal and ventral regions of PPC and suggest that the dorsal PPC may support the spatial coding of the visual environment even when this information is incidental to the task at hand. Further, through revealing the differential functional interactions of the SPG and AG with the MTL our results help advance our understanding of how the MTL and PPC cooperate to update representations of the world around us.
Dorsal Versus Ventral Anterior Urethral Spatulation in Posterior Urethroplasty  [cached]
Jalil Hosseini,Mohammad Jabbari,Ali Kaviani,Mohammad Mohsen Mazloomfard
Urology Journal , 2010,
Abstract: PURPOSE: To compare dorsal versus ventral anterior urethral spatulation in posterior urethroplasty. MATERIALS AND METHODS: In a retrospective study, we evaluated the records of 320 posterior urethroplasties which have been done in our center over a 7-year period from January 2000 to December 2006. The results of dorsal and ventral anterior urethral spatulations were compared. RESULTS: The studied subjects consisted of 264 men and 54 prepubescent boys (≤ 15 years) with the mean age of 23 years (range, 5 to 84 years). The mean follow-up was 52 months (range, 27 to 107 months). Six o’clock (group A) and 12 o’clock (group B) anterior urethral spatulations were performed in 101 (32%) and 219 (68%) of the patients, respectively. The success rates were 96% and 87.6% in groups A and B, respectively (P = .025). There wereno urethro-rectal fistula and perineal wound infection during the follow-up period. CONCLUSION: Our data suggest that the dorsal anterior urethral spatulation in urethroplasty is more efficient than ventral anterior urethral spatulation in terms of treatment success outcome.
Postoperative studies following ventral and dorsal cystotomy in mongrel dogs
SC Akomas, ROC Kene
Nigerian Veterinary Journal , 2003,
Abstract: There was omental adhesion in both the dorsal and ventral approaches to the urinary bladder. Adhesion involving the small intestine and colon were also observed. There was however no urine leakage into the peritoneal cavity following either of the approaches. The incision wounds were also seen to have healed by the fourteen postoperative day when the postmortem studies were carried out. KEY WORDS: Cystotomy, incisions, postoperative, adhesions, dogs Nigerian Veterinary Journal Vol.24(2) 2003: 52-56
Organization of Multisynaptic Inputs to the Dorsal and Ventral Dentate Gyrus: Retrograde Trans-Synaptic Tracing with Rabies Virus Vector in the Rat  [PDF]
Shinya Ohara, Sho Sato, Ken-Ichiro Tsutsui, Menno P. Witter, Toshio Iijima
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0078928
Abstract: Behavioral, anatomical, and gene expression studies have shown functional dissociations between the dorsal and ventral hippocampus with regard to their involvement in spatial cognition, emotion, and stress. In this study we examined the difference of the multisynaptic inputs to the dorsal and ventral dentate gyrus (DG) in the rat by using retrograde trans-synaptic tracing of recombinant rabies virus vectors. Three days after the vectors were injected into the dorsal or ventral DG, monosynaptic neuronal labeling was present in the entorhinal cortex, medial septum, diagonal band, and supramammillary nucleus, each of which is known to project to the DG directly. As in previous tracing studies, topographical patterns related to the dorsal and ventral DG were seen in these regions. Five days after infection, more of the neurons in these regions were labeled and labeled neurons were also seen in cortical and subcortical regions, including the piriform and medial prefrontal cortices, the endopiriform nucleus, the claustrum, the cortical amygdala, the medial raphe nucleus, the medial habenular nucleus, the interpeduncular nucleus, and the lateral septum. As in the monosynaptically labeled regions, a topographical distribution of labeled neurons was evident in most of these disynaptically labeled regions. These data indicate that the cortical and subcortical inputs to the dorsal and ventral DG are conveyed through parallel disynaptic pathways. This second-order input difference in the dorsal and ventral DG is likely to contribute to the functional differentiation of the hippocampus along the dorsoventral axis.
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