The isocortex is a distinctive feature of mammalian brains, which has no clear counterpart in the cerebral hemispheres of other amniotes. This paper speculates on the evolutionary processes giving rise to the isocortex. As a first step, we intend to identify what structure may be ancestral to the isocortex in the reptilian brain. Then, it is necessary to account for the transformations (developmental, connectional, and functional) of this ancestral structure, which resulted in the origin of the isocortex. One long-held perspective (...) argues that part of the isocortex derives from the ventral pallium of reptiles, whereas another view proposes that the isocortex originated mostly from the dorsal pallium. We consider that, at this point, evidence tends to favor correspondence of the isocortex with the dorsal cortex of reptiles. In any case, the isocortex may have originated partly as a consequence of an overall “dorsalizing” effect (that is, an expansion of the territories expressing dorsal-specific genes) during pallial development. Furthermore, expansion of the dorsal pallium may have been driven by selective pressures favoring the development of associative networks between the dorsal cortex, the olfactory cortex, and the hippocampus, which participated in spatial or episodic memory in the early mammals. In this context, sensory projections that in reptiles end in the ventral pallium, are observed to terminate in the isocortex (dorsal pallium) of mammals, perhaps owing to their participation in these associative networks. Key Words: basolateral amygdala; claustrum; Emx-1; endopiriform nucleus; dorsal cortex; dorsal ventricular ridge; hippocampus; homology; olfactory cortex; Pax-6; ventral pallium. (shrink)

A dorsalization mechanism is a good candidate for the evolutionary origin of the isocortex, producing a radial and tangential expansion of the dorsal pallium (and perhaps other structures that acquired a cortical phenotype). Evidence suggests that a large part of the dorsal ventricular ridge (DVR) of reptiles and birds derives from the embryonic ventral pallium, whereas the isocortex possibly derives mostly from the dorsal pallium. In early mammals, the development of olfactory-hippocampal associative networks may have been (...) pivotal in facilitating the selection of a larger and more complex dorsal pallium which received both collothalamic and lemnothalamic sensory information. Finally, although it is not clear exactly when mammalian brain expansion began, fossil evidence indicates that this was a late event in mammaliaform evolution. (shrink)

Opposed to Norman's proposal, processing of affordance is likely to occur not solely in the dorsal stream but also in the ventral stream. Moreover, the dorsal stream might do more than just serve an important role in motor actions. It supports egocentric location coding as well. As such, it would possess a form of representational memory, contrary to Norman's proposal.

The ventral lateral parietal cortex shows robust activation during episodic retrieval, and is involved in content representation, as well as in the evaluation of memory traces. This suggests that the VLPC has a crucial contribution to the quality of recollection and the subjective experience of remembering, and situates it at the intersection of the core and attribution systems.

Experimental data suggest that the division between the visual ventral and dorsal pathways may indeed indicate that static and dynamical information is processed separately. Contrary to Hurford, it is suggested that the ventral pathway primarily generates representations of objects, whereas the dorsal pathway produces representations of events. The semantic object/event distinction may relate to the morpho-syntactic noun/verb distinction.

Molecular and developmental studies of limb pattern formation have recently gained widespread attention. The fact that vertebrate limbs are amenable to both genetic and embryological manipulations has established this model system as a valuable paradigm for studying vertebrate development. Limb buds are polarised along all three major axes and the establishment of the dorso‐ventral (DV) polarity is dependent upon cues localised in the trunk, where a DV ectodermal interface is produced by confrontation of dorsal and ventral identities. By (...) analogy to Drosophila imaginal disc development, this interface has been proposed to determine and position an ectodermal organising centre, the Apical Ectodermal Ridge (AER), controlling limb bud outgrowth. Recent fate mapping studies(1) and studies of genes regulating DV limb polarity(2‐6), AER formation(7,8) and differentiation(9) suggest, however, that DV patterning and AER induction, though coordinately regulated during limb bud outgrowth, may early on be more dissociated than expected. (shrink)

It is necessary to distinguish among representations caused directly by perception, representations of past perceptions in long-term memory, the representations underlying linguis- tic utterances, and the surface phonological and grammatical structures of sentences. The target article dealt essentially with predicate-argument structure at the first of these levels of representation. Discussion of the commentaries mainly involves distinguishing among various applications of the term “predicate”; clarifying the assumed relationship between classical FOPL and language; clarifying the status of unique individuals as conceived by (...) humans; and addressing the issues of motion-perception, binding between object-percepts and predicate-percepts, and target-driven versus stimulus-driven attention. (shrink)

Adolescence has been linked to an enhanced tolerance of uncertainty and risky behavior and is possibly connected to an increased response toward rewards. However, previous research has produced inconsistent findings. To investigate whether these findings are due to different reward probabilities used in the experimental design, we extended a monetary incentive delay task by including three different reward probabilities. Using functional magnetic resonance imaging, 25 healthy adolescents and 22 adults were studied during anticipation of rewards in the VS. Differently colored (...) cue stimuli indicated either a monetary or verbal trial and symbolized different reward probabilities, to which the participants were blinded. Results demonstrated faster reaction times for lower reward probabilities in both age groups. Adolescents were slower through all conditions and had less activation on a neural level. Imaging results showed a three-way interaction between age group x condition x reward probability with differences in percent signal change between adolescents and adults for the high reward probabilities while adolescents demonstrated differences for the lowest. Therefore, previous inconsistent findings could be due to different reward probabilities, which makes examining these crucial for a better understanding of adolescent and adult behavior. (shrink)

The author argues that the theory of a dorsal/ventral stream for visual processing can be used to reconcile the constructivist and direct perception theories. My commentary discusses neurophysiological and psychophysical studies that run counter to the view. In addition, the central issue of debate between the constructionist and direct perception approaches regarding what is visual information is discussed.

Several lines of evidence indicate that rapid target-aiming movements, involving both the eyes and hand, can be biased by the visual context in which the movements are performed. Some of these contextual influences carry-over from trial to trial. This research indicates that dissociation between the dorsal and ventral systems based on speed, conscious awareness, and frame of reference is far from clear.

The exact relationship between qualia and the function of the brain remains elusive. The present approach focuses on the linkage between the neural mechanisms of the brain and the phenomenological and epistemological mechanisms of qualia. It is hypothesized that distinct characteristics of the ventral prefrontal cortical function may be crucial for the generation of these phenomenological and epistemological mechanisms this is reflected in the so-called 'neurophenomenological hypothesis'. The 'phenomenological—qualitative' character of qualia may be related with an early activation in (...) the ventromedial prefrontal cortex . The experience of 'presence' in qualia may be accounted for by a co-activation in both VMPFC and hippocampus and a concurrent deactivation in the ventrolateral prefrontal cortex and posterior cingulate. Past and future temporal dimensions may therefore be integrated within the experience of events, which in turn may account for the phenomenal characteristics of 'presence' and thus 'phenomenal time'. 'Non-structural homogeneity' in the experience of qualia may be accounted for by either 'supramodal character' or 'modality unspecifity' of >the VMPFC. The 'heterogenous' stimuli can therefore be included and integrated within one 'homogenous' event as experienced in qualia. Finally, 'transparency' in the experience of qualia may be related with the 'reciprocal suppression' between VMPFC and VLPFC. Simultaneous cognitive processing during the experience of qualia may be suppressed and may consequently account for their transparent character. Due to several methodological limitations, these 'neurophenomenological hypotheses' must be considered as preliminary. However, they may nevertheless serve as a starting point for the development of a more elaborate neuroscientific hypothesis of qualia in the future. (shrink)

Scaling of pattern with size has been described and studied for over a century, yet its molecular basis is understood in only a few cases. In a recent, elegant study, Inomata and colleagues proposed a new model explaining how bone morphogenic protein (BMP) activity gradient scales with embryo size in the early Xenopus laevis embryo. We discuss their results in conjunction with an alternative model we proposed previously. The expansion‐repression mechanism (ExR) provides a conceptual framework unifying both mechanisms. Results of (...) Inomata and colleagues implicate the chordin‐stabilizing protein sizzled as the expander molecule enabling scaling, while we attributed this role to the BMP ligand Admp. The two expanders may work in concert, as suggested by the mathematical model of Inomata et al. We discuss approaches for differentiating the contribution of sizzled and Admp to pattern scaling. (shrink)

Bowers et al. rightly emphasise that deep learning models often fail to capture constraints on visual perception that have been discovered by previous research. However, the solution is not to discard deep learning altogether, but to design stimuli and tasks that more closely reflect the problems that biological vision evolved to solve, such as understanding scenes and preparing skilled action.

Everyday life suggests that picture seeing is sometimes infused by an emotional charge. However, nobody has addressed the importance of explaining this emotional charge in picture perception. Even our best model of picture perception, the dorsal/ventral account of picture perception, which integrates the most important empirical results coming from our best model on vision in neuroscience, the two visual systems model, lacks a reference to this emotional charge. The aim of the present paper is to offer an account of (...) picture perception that is able to regain and explain this neglected emotional charge. My claim is that, as for face-to-face perception, during picture perception, we are not only in a visual perceptual state, but also in an emotional state, which is directly connected to our visual perceptual state. I also show that it is possible to offer this integration while remaining in the philosophical/empirical framework of the dorsal/ventral account of picture perception, whose explanatory power is confirmed and improved. (shrink)

Norman's identification of a ventral system embodying a constructivist theory of perception is rejected in favor of an ecological theory of perception and perceptual learning. We summarize research showing that a key motivation for the ventral-constructivist connection, percept-percept coupling, confuses perceptual and post-perceptual processes.

Patients with apraxia perform poorly when demonstrating how an object is used, particularly when pantomiming the action. However, these patients are able to accurately identify, and to pick up and move objects, demonstrating intact ventral and dorsal stream visuomotor processing. Appropriate object manipulation for skilled use is thought to rely on integration of known and visible object properties associated with ‘ventro-dorsal’ stream neural processes. In apraxia, it has been suggested that stored object knowledge from the ventral stream may (...) be less readily available to incorporate into the action plan, leading to an over-reliance on the objects’ visual affordances in object-directed motor behaviour. The current study examined grasping performance in left hemisphere stroke patients with (N = 3) and without (N = 9) apraxia, and in age-matched healthy control participants (N = 14), where participants repeatedly grasped novel cylindrical objects of varying weight distribution. Across two conditions, object weight distribution was indicated by either a memory-associated cue (object colour) or visual-spatial cue (visible dot over the weighted end). Participants were required to incorporate object-weight associations to effectively grasp and balance each object. Control groups appropriately adjusted their grasp according to each object’s weight distribution across each condition, whereas throughout the task two of the three apraxic patients performed poorly on both the memory-associated and visual-spatial cue conditions. A third apraxic patient seemed to compensate for these difficulties but still performed differently to control groups. Patients with apraxia performed normally on the neutral control condition when grasping the evenly weighted version. The pattern of behaviour in apraxic patients suggests impaired integration of visible and known object properties attributed to the ventro-dorsal stream: in learning to grasp the weighted object accurately, apraxic patients applied neither pure knowledge-based information (the memory-associated condition) nor higher-level information given in the visual-spatial cue condition. Disruption to ventro-dorsal stream predicts that apraxic patients will have difficulty learning to manipulate new objects on the basis of information other than low-level visual cues such as shape and size. (shrink)

While there has been a lot of discussion of picture perception both in perceptual psychology and in philosophy, these discussions are driven by very different background assumptions. Nonetheless, it would be mutually beneficial to arrive at an understanding of picture perception that is informed by both the philosophers’ and the psychologists’ story. The aim of this paper is exactly this: to give an account of picture perception that is valid both as a philosophical and as a psychological account. I argue (...) that seeing trompe l’oeil paintings is, just as some philosophers suggested, different from other cases of picture perception. Further, the way our perceptual system functions when seeing trompe l’oeil paintings could be an important piece of the psychological explanation of perceiving pictures. (shrink)

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The dorsal and medial pallial formations of mammals, birds, and reptiles show overall functional striking similarities. Most of these similarities have been frequently considered examples of convergent evolution. However, a considerable amount of neurobiological comparative evidence suggests the presence of a common basic pattern of vertebrate forebrain organization. This common pattern can support functional conservation.

Deep brain stimulation is a clinical intervention for the treatment of movement disorders. It has also been applied to the treatment of psychiatric disorders such as depression, anorexia nervosa, obsessive-compulsive disorder, and schizophrenia. Psychiatric disorders including schizophrenia, bipolar disorder, and major depression can lead to psychosis, which can cause patients to lose touch with reality. The ventral tegmental area, located near the midline of the midbrain, is an important region involved in psychosis. However, the clinical application of electrical stimulation (...) of the VTA to treat psychotic diseases has been limited, and related mechanisms have not been thoroughly studied. In the present study, hyperlocomotion and stereotyped behaviors of the mice were employed to mimic and evaluate the positive-psychotic-like behaviors. We attempted to treat positive psychotic-like behaviors by electrically stimulating the VTA in mice and exploring the neural mechanisms behind behavioral effects. Local field potential recording and in vivo fiber photometry to observe the behavioral effects and changes in neural activities caused by DBS in the VTA of mice. Optogenetic techniques were used to verify the neural mechanisms underlying the behavioral effects induced by DBS. Our results showed that electrical stimulation of the VTA activates local gamma-aminobutyric acid neurons, and dopamine neurons, reduces hyperlocomotion, and relieves stereotyped behaviors induced by MK-801 injection. The results of optogenetic manipulation showed that the activation of the VTA GABA neurons, but not DA neurons, is involved in the alleviation of hyperlocomotion and stereotyped behaviors. We visualized changes in the activity of specific types in specific brain areas induced by DBS, and explored the neural mechanism of DBS in alleviating positive psychotic-like behaviors. This preclinical study not only proposes new technical means of exploring the mechanism of DBS, but also provides experimental justification for the clinical treatment of psychotic diseases by electrical stimulation of the VTA. (shrink)

Malformations concerning the ventral body wall constitute one of the leading categories of human birth defects and are present in about one out of every 2000 live births. Although the occurrence of these defects is relatively common, few detailed experimental studies exist on the development and closure of the ventral body wall in mouse and human. This field is further complicated by the array of theories on the pathogenesis of body wall defects and the likelihood that there is (...) no single cause for these abnormalities. In this review, we summarize what is known concerning the mechanisms of normal ventral body wall closure in humans and mice. We then outline the theories that have been proposed concerning human body wall closure abnormalities and examine the growing number of mouse mutations that impact normal ventral body wall closure. Finally, we speculate how studies in animal models such as mouse and Drosophila are beginning to provide a much‐needed mechanistic framework with which to identify and characterize the genes and tissues required for this vital aspect of human embryogenesis. BioEssays 26:1307–1321, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Support for the proposed dorsal-ventral distinction for the somatosensory system is not yet convincing, nor is the anatomical segregation of its pathways as clearly defined as the visual pathways. Consideration of alternative organizational principles might reveal critical differences across sensory processing systems. The role of attention and manipulations that modulate functional systems might also be worth considering.