On the emergence of primary visual perception.

We propose a concise novel conceptual and biological framework for the analysis of primary visual perception (PVP) that refers to the most basic levels of our awake subjective visual experiences. Neural representations for image content elaborated within V1/V2 and the early occipitotemporal (ventral) loop remain only latent with respect to PVP until spatially localized with respect to an attending observer. This process requires more than the downstream deployment of attentional resources onto targeted neurons.

Long-term statin therapy and CSF cholesterol levels: implications for Alzheimer's disease.

Background/aims: It is not yet established whether statins (lipophilic or hydrophilic) reduce the risk of Alzheimer's disease and, if so, by differentially modifying brain lipid levels. Our aim was to assess changes in brain cholesterol metabolism as reflected in the cerebrospinal fluid (CSF) before and after treatment with either atorvastatin or simvastatin.

Methods: We carried out a longitudinal analysis of CSF cholesterol, lathosterol and 24(S)-hydroxycholesterol before and after treatment with maximum doses of statins in 10 asymptomatic subjects, 8 of whom were heterozygous for apolipoprotein E epsilon4, and in 6 presymptomatic PS1 subjects.

Fundamental requirements for primary visual perception.

A novel perspective for the necessary and sufficient conditions for primary visual perception is proposed based upon relating recent discoveries from the visual sciences to relevant foundational neurological observations. This analysis suggests that a fundamental requirement for the emergence of normal primary visual perception is the coupling between the early visual cortices in the occipital lobe subserving image content with specific areas in the parietal lobe subserving selective attention, representations of extrapersonal space, the body schema, and the initiation of perceptual ownership. Fully intact primary visual perception, which includes the normal placement of image content within extrapersonal space, seems to require at each instant a mutually consistent completeness and corresponding removal of ambiguities in each of the linked neural representations subserving image, space and self.

Amyloid deposition begins in the striatum of presenilin-1 mutation carriers from two unrelated pedigrees.

The amyloid cascade hypothesis suggests that the aggregation and deposition of amyloid-beta protein is an initiating event in Alzheimer's disease (AD). Using amyloid imaging technology, such as the positron emission tomography (PET) agent Pittsburgh compound-B (PiB), it is possible to explore the natural history of preclinical amyloid deposition in people at high risk for AD. With this goal in mind, asymptomatic (n = 5) and symptomatic (n = 5) carriers of presenilin-1 (PS1) mutations (C410Y or A426P) that lead to early-onset AD and noncarrier controls from both kindreds (n = 2) were studied with PiB-PET imaging and compared with sporadic AD subjects (n = 12) and controls from the general population (n = 18).

Brain stimulation and conscious experience: electrical stimulation of the cortical surface at a threshold current evokes sustained neuronal activity only after a prolonged latency.

Libet demonstrated that a substantial duration (>0.5-1.0 s) of direct electrical stimulation of the surface of a sensory cortex at a threshold or liminal current is required before a subject can experience a percept.

Brain stimulation and conscious experience.

Libet discovered that a substantial duration (> 0.5-1.0 s) of direct electrical stimulation of the surface of the somatosensory cortex at threshold currents is required before human subjects can report that a conscious somatosensory experience had occurred.

Explicit neural representations, recursive neural networks and conscious visual perception.

The fundamental question as to whether the neural correlates of any given conscious visual experience are expressed locally within a given cortical area or more globally within some widely distributed network remains unresolved. We inquire as to whether recursive processing-by which we mean the combined flow and integrated outcome of afferent and recurrent activity across a series of cortical areas-is essential for the emergence of conscious visual experience. If so, we further inquire as to whether such recursive processing is essential only for loops between extrastriate cortical areas explicitly representing experiences such as color or motion back to V1 or whether it is processing between still higher levels and the areas computing such explicit representations that is exclusively or additionally essential for visual experience.

Spatial receptive field organization of macaque V4 neurons.

Subfield analysis of the receptive fields (RFs) of parafoveal V4 complex cells demonstrates directly that most RFs are tiled by overlapping second-order excitatory inputs that for any given V4 cell are predominantly selective to the same preferred values of spatial frequency and orientation. These results extend hierarchical principles of RF organization in the spatial, orientation and spatial frequency domains, first recognized in V1, to an intermediate extrastriate cortex. Spatial interaction studies across subfields demonstrate that the responses of V4 neurons to paired stimuli may either decrease or increase as a function of inter-stimulus distance across the width axis.