Rate of tree carbon accumulation increases continuously with tree size.

Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle--particularly net primary productivity and carbon storage--increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree's total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.

Vitamin B12 deficiency associated with symptoms of frontotemporal dementia.

We report the case of an elderly patient with cobalamin deficiency who progressively developed cognitive and behavioral symptoms associated with neuropsychiatric disturbances. His neuropsychological profile showed many features suggestive for a frontal-dysexecutive syndrome and was related to a predominant asymmetric (right > left) frontal lobe hypoperfusion. He completely recovered after a treatment with vitamin B12 and follow-up of 7 years showed that his improvement remained stable. Along with the other cases reported in the literature, our case also proves that there are some cases of vitamin B12 deficiency that can manifest with the symptoms of frontotemporal dementia and that they are completely reversible after substitution therapy.

Perception of ambiguous figures after focal brain lesions.

Forty patients with unilateral frontal or posterior brain damage and 20 normal control subjects were tested on an ambiguous figures task (AFT). For each figure they were asked to recognize both ambiguous images. Subjects failing to recognize the second aspect of an ambiguous figure were prompted with the name of the image not yet perceived. The Wisconsin Card Sorting Test (WCST) was also administered to all subjects. Frontal patients exhibited greater difficulty in shifting from one aspect of an ambiguous figure to the other than did patients with more posterior lesions and control subjects. In addition, frontal-posterior and control differences were highly significant for number of prompts given. For the frontal patients, significant correlations were found between the number of prompts on the AFT and the number of perseverative errors on the WCST. Poor performance on the AFT can be considered as a "frontal lobe sign" of perceptual persevation.

Surgical treatment of the distal anterior cerebral artery aneurysms.

A series of eleven patients with aneurysms of distal anterior cerebral artery, microsurgically operated and submitted to accurate neuropsychological testing, is reviewed. Of these, ten patients had an aneurysm at the bifurcation of distal ACA into pericallosal and callosomarginal branches and only one patient had an aneurysm at the beginning of the fronto-polar artery. All our patients were operated by an interhemispheric approach, that was associated in 3 cases to a pterional approach in order to clip a second aneurysm in other location. The postoperative grade was satisfactory in any of the eleven patients. The aneurysms of distal ACA may be surgically obliterated through a variety of approaches but the exposure via the interhemispheric fissure is used by many neurosurgeons. In our experience the interhemispheric approach allows the exposure of feeding artery and the control of proximal vessel without morbidity. Some authors have modified the interhemispheric approach to improve, in their opinion, surgical exposure, introducing partial resection of anterior portion of corpus callosum, used, by them, especially for the aneurysms just beneath the genu of corpus callosum. Although resection of the anterior 2.5 cm of the corpus callosum can be performed without causing any neurological deficit, as reported by the same authors, the use of this technique might not be necessary. The present paper deals with current surgical techniques and their modification for the treatment of distal anterior cerebral artery (ACA) aneurysms.

A selective egocentric topographical working memory deficit in the early stages of Alzheimer's disease: a preliminary study.

The aim of this study was to determine whether an egocentric topographical working memory (WM) deficit is present in the early stages of Alzheimer's disease (AD) with respect to other forms of visuospatial WM. Further, we would investigate whether this deficit could be present in patients having AD without topographical disorientation (TD) signs in everyday life assessed through an informal interview to caregivers. Seven patients with AD and 20 healthy participants performed the Walking Corsi Test and the Corsi Block-Tapping Test. The former test requires memorizing a sequence of places by following a path and the latter is a well-known visuospatial memory task. Patients with AD also performed a verbal WM test to exclude the presence of general WM impairments. Preliminary results suggest that egocentric topographical WM is selectively impaired, with respect to visuospatial and verbal WM, even without TD suggesting an important role of this memory in the early stages of AD.

The indocyanine green method is equivalent to the 99mTc-labeled radiotracer method for identifying the sentinel node in breast cancer: a concordance and validation study.

AIMS: The aim of this study was to assess concordance between the indocyanine green (ICG) method and (99m)Tc-radiotracer method to identify the sentinel node (SN) in breast cancer. Evidence supports the feasibility and efficacy of the ICG to identify the SN, however this method has not been prospectively compared with the gold-standard radiotracer method in terms of SN detection rate. METHODS: Between June 2011 and January 2013, 134 women with clinically node-negative early breast cancer received subdermal/peritumoral injection of (99m)Tc-labeled tracer for lymphoscintigraphy, followed by intraoperative injection of ICG for fluorescence detection of SNs using an exciting light source combined with a camera. In all patients, SNs were first identified by the fluorescence method (ICG-positive) and removed. A gamma ray-detecting probe was then used to determine whether ICG-positive SNs were hot ((99m)Tc-positive) and to identify and remove any (99m)Tc-positive (ICG-negative) SNs remaining in the axilla. The study was powered to perform an equivalence analysis. RESULTS: The 134 patients provided 246 SNs, detected by one or both methods. 1, 2 and 3 SNs, respectively, were detected, removed and examined in 70 (52.2%), 39 (29.1%) and 17 (12.7%) patients; 4-10 SNs were detected and examined in the remaining 8 patients. The two methods were concordant for 230/246 (93.5%) SNs and discordant for 16 (6.5%) SNs. The ICG method detected 99.6% of all SNs. CONCLUSIONS: Fluorescent lymphangiography with ICG allows easy identification of axillary SNs, at a frequency not inferior to that of radiotracer, and can be used alone to reliably identify SNs.

When, where, and how the corpus callosum changes in MCI and AD: a multimodal MRI study.

BACKGROUND: The corpus callosum (CC) has been shown to be susceptible to atrophy in Alzheimer disease (AD) as a correlate of wallerian degeneration or retrogenesis. However, when and where these 2 mechanisms intervene is still unclear. METHODS: In 3 memory clinics, we recruited 38 patients with amnestic mild cognitive impairment (MCI), 38 patients with mild AD, and 40 healthy controls (HC). Combining voxel-based morphometry and diffusion tensor imaging, we investigated CC white matter (WM) density and fractional anisotropy (FA), radial diffusivity (DR), and axial diffusivity (DA). RESULTS: Compared with HC, patients with amnestic MCI showed reduced WM density in the anterior CC subregion; however, FA, DR, and DA did not differ between the 2 groups. Significant changes were found in patients with mild AD compared with HC in the anterior and posterior CC regions. These differences were evident in both voxel-based morphometry and diffusion tensor imaging analyses. Specifically, we found reduced callosal WM density in the genu, posterior body, and splenium; decreased FA and increased DR in the anterior CC subregion; and increased DA, with no difference in the FA, in the posterior CC subregion. CONCLUSIONS: Callosal changes are already present in patients with amnestic mild cognitive impairment (MCI) and mild Alzheimer disease (AD). The precocious involvement of the anterior callosal subregion in amnestic MCI extends to posterior regions in mild AD. Two different mechanisms might contribute to the white matter changes in mild AD: wallerian degeneration in posterior subregions of the corpus callosum (suggested by increased axial diffusivity without fractional anisotropy modifications) and a retrogenesis process in the anterior callosal subregions (suggested by increased radial diffusivity without axial diffusivity modifications).

Avoidance conditioning in amnesia: a single case experimental study.

We present a single case study of avoidance conditioning in a seriously amnesic patient with bilateral ischemic lesions of the brain. A four-path maze was used for conditioning. The procedure consisted in an aversive stimulus that the patient received every time he traced one of the four maze-paths connected to an electric shock generator with a stylus. Using a single case experimental design A-B-A, we found that the patient learned to avoid the path connected to the electric shock, although he never showed awareness of this. Our study confirms once again that conditioning is one of the residual learning capabilities in amnesic patients. Different neural systems are probably involved in conditioning processes.