汉字阅读加工的功能磁共振研究进展

对阅读基本机制的了解是研究失读症发病机制和对失读症进行康复治疗的基础。功能磁共振成像是一种能显示活体脑内神经活动状态的成像方法,近年来被用于语言学尤其是汉字阅读加工机制的研究。本文对汉字单字加工的偏侧化以及是否存在汉字认知加工的特异脑区等进行综述。     

Effects of cholinergic deafferentation of the rhinal cortex on visual recognition memory in monkeys

Excitotoxic lesion studies have confirmed that the rhinal cortex is essential for visual recognition ability in monkeys. To evaluate the mnemonic role of cholinergic inputs to this cortical region, we compared the visual recognition performance of monkeys given rhinal cortex infusions of a selective cholinergic immunotoxin, ME20.4-SAP, with the performance of monkeys given control infusions into this same tissue. The immunotoxin, which leads to selective cholinergic deafferentation of the infused cortex, yielded recognition deficits of the same magnitude as those produced by excitotoxic lesions of this region, providing the most direct demonstration to date that cholinergic activation of the rhinal cortex is essential for storing the representations of new visual stimuli and thereby enabling their later recognition.     

Topographic organization of macaque area LIP

Despite several attempts to define retinotopic maps in the macaque lateral intraparietal area (LIP) using histological, electrophysiological, and neuroimaging methods, the degree to which this area is topographically organized remains controversial. We recorded blood oxygenation level–dependent signals with functional MRI from two macaques performing a difficult visual search task on stimuli presented at the fovea or in the periphery of the visual field. The results revealed the presence of a single topographic representation of the contralateral hemifield in the ventral subdivision of the LIP (LIPv) in both hemispheres of both monkeys. Also, a foveal representation was localized in rostral LIPv rather than in dorsal LIP (LIPd) as previous experiments had suggested. Finally, both LIPd and LIPv responded only to contralateral stimuli. In contrast, human studies have reported multiple topographic maps in intraparietal cortex and robust responses to ipsilateral stimuli. These blood oxygenation level–dependent functional MRI results provide clear evidence for the topographic organization of macaque LIP that complements the results of previous electrophysiology studies, and also reveal some unexpected characteristics of this organization that have eluded these previous studies. The results also delineate organizational differences between LIPv and LIPd, providing support for these two histologically defined areas may subserve different visuospatial functions. Finally, these findings point to potential evolutionary differences in functional organization with human posterior parietal cortex.     

Top-down attention switches coupling between low-level and high-level areas of human visual cortex

Top-down attention is an essential cognitive ability, allowing our finite brains to process complex natural environments by prioritizing information relevant to our goals. Previous evidence suggests that top-down attention operates by modulating stimulus-evoked neural activity within visual areas specialized for processing goal-relevant information. We show that top-down attention also has a separate influence on the background coupling between visual areas: adopting different attentional goals resulted in specific patterns of noise correlations in the visual system, whereby intrinsic activity in the same set of low-level areas was shared with only those high-level areas relevant to the current goal. These changes occurred independently of evoked activity, persisted without visual stimulation, and predicted behavioral success in deploying attention better than the modulation of evoked activity. This attentional switching of background connectivity suggests that attention may help synchronize different levels of the visual processing hierarchy, forming state-dependent functional pathways in human visual cortex to prioritize goal-relevant information.     

难治性枕叶癫痫的手术治疗（附7例报告）

目的分析难治性枕叶癫痫的手术治疗效果和视觉功能保护效果。方法对7例难治性枕叶癫痫患者,行视力视野检查,致痫灶行皮层或局部病灶及周围胶质增生带切除术,对5~10 s内迅速跟随发作起始的症状产生区行低功率皮层热灼术或局部皮层切除术,疑有功能区放电或发作起始者加行脑磁图功能区定位,功能区行低功率皮层热灼术,并注意保护好其白质传导纤维。其中确定发作起始于功能区的2例行功能区皮层热灼术。根据Engel′s术后效果分级评估疗效;行视力视野检查,观察术后患者视觉功能变化。结果术后随访6-12个月,6例无癫痫发作,达到Engel′sⅠ级,1例术后存在稀少癫痫发作,达到Engel′sⅡ级。6例（包括行功能区皮层热灼术2例）术后视觉功能无明显变化,1例视觉功能障碍较术前加重。结论定位明确的难治性枕叶癫痫患者可行致痫灶皮层或局部病灶及周围胶质增生带切除术;功能区低功率皮层热灼术可有效控制癫痫发作,且不造成功能缺失。术前精确定位功能区,术中保护功能区皮质及白质传导纤维,可有效减少视觉功能损伤机会。     

Functional and structural architecture of the human dorsal frontoparietal attention network

The dorsal frontoparietal attention network has been subdivided into at least eight areas in humans. However, the circuitry linking these areas and the functions of different circuit paths remain unclear. Using a combination of neuroimaging techniques to map spatial representations in frontoparietal areas, their functional interactions, and structural connections, we demonstrate different pathways across human dorsal frontoparietal cortex for the control of spatial attention. Our results are consistent with these pathways computing object-centered and/or viewer-centered representations of attentional priorities depending on task requirements. Our findings provide an organizing principle for the frontoparietal attention network, where distinct pathways between frontal and parietal regions contribute to multiple spatial representations, enabling flexible selection of behaviorally relevant information.Visual scenes usually contain many different objects, which cannot all be processed simultaneously because of the limited capacity of the visual system. Attention mechanisms are thus needed to select the most behaviorally relevant information for further processing. Previous studies have demonstrated activations over large portions of dorsal frontoparietal cortex during a variety of selective attention tasks (1, 2). In humans, these regions include intraparietal sulcus areas 1–5 (IPS1–IPS5) and superior parietal lobule area 1 (SPL1) in posterior parietal cortex (PPC), defined by spatial topographic mapping (3, 4), as well as the frontal eye field (FEF) and the putative human supplementary eye field (SEF) in frontal cortex (Fig. S1). Although these areas are commonly conceptualized as a frontoparietal attention network, the circuitry linking areas, the functions of different circuit paths, and the different roles of individual areas in representing attentional priorities remain unclear.Because everyday actions rely on representations of attentional priorities in egocentric (gaze-centered, body-centered) and allocentric (object-centered, world-centered) spatial reference frames (5–9)—for example, to pick up a coffee cup, we must know where the cup is relative to our body, as well as where the handle is relative to the cup—we need to flexibly specify and read out attentional priorities in different reference frames. However, human neuroimaging studies have largely focused on gaze-centered representations and have been relatively unsuccessful in finding representations in other spatial reference frames, perhaps because they have focused on visual cortex (e.g., refs. 10 and 11). In frontoparietal cortex, the topographic organization of IPS1-5, SPL1, and FEF suggests that they contain spatial representations at least in egocentric reference frames (3, 12, 13). In contrast, human SEF lacks a clear topography (Fig. S1; refs. 14–16). Macaque SEF also lacks a clear topography (17, 18), although macaque SEF neurons have been shown to represent space in gaze-centered as well as head-, body-, and object-centered reference frames (9, 19). This diversity in macaque SEF neuronal responses suggests that the human SEF may be able to represent space in multiple reference frames as well.Different inputs from IPS1-5 and SPL1 may contribute to the difference in functional organization between the FEF and SEF. In macaque monkeys, PPC subdivisions contain different proportions of neurons representing space in egocentric, allocentric, or intermediate reference frames (20–24). Computational studies have shown that it is possible to combine outputs from such neurons to perform different spatial transformations (25). Thus, distinct pathways from parietal areas to frontal cortex could give rise to the representation of attentional priorities in a number of different reference frames. Analyzing functional and structural connectivity in frontoparietal circuits might therefore be a useful approach to study different spatial representations. Here, we used a combination of topographic mapping, functional connectivity analyses of functional magnetic resonance imaging (fMRI) data, and structural connectivity analyses using diffusion MRI (dMRI) to test the hypotheses that: (i) there are distinct functional pathways within the dorsal frontoparietal attention network, (ii) these pathways support different spatial representations of attentional priorities, and (iii) structural connectivity between dorsal frontal and parietal areas supports this functionality. Our findings demonstrate that the FEF and SEF form distinct pathways to parietal areas, consistent with roles in enabling the specification and readout of attentional priorities in egocentric and allocentric reference frames.     

基于模块化的主观认知减退人群静息态皮质网络连接组学研究

目的:探讨主观认知减退（SCD）人群静息态皮质网络的拓扑特征及与认知水平的相关性。方法:收集2017年6月至2019年11月在南京各社区招募36例自诉有记忆下降的中老年人与32名健康对照（NC）,分析认知量表、T 1加权像（T 1WI）和静息态功能磁共振（rs-fMRI）数据。SCD组男5例、女...     

Acuity-independent effects of visual deprivation on human visual cortex

Visual development depends on sensory input during an early developmental critical period. Deviation of the pointing direction of the two eyes (strabismus) or chronic optical blur (anisometropia) separately and together can disrupt the formation of normal binocular interactions and the development of spatial processing, leading to a loss of stereopsis and visual acuity known as amblyopia. To shed new light on how these two different forms of visual deprivation affect the development of visual cortex, we used event-related potentials (ERPs) to study the temporal evolution of visual responses in patients who had experienced either strabismus or anisometropia early in life. To make a specific statement about the locus of deprivation effects, we took advantage of a stimulation paradigm in which we could measure deprivation effects that arise either before or after a configuration-specific response to illusory contours (ICs). Extraction of ICs is known to first occur in extrastriate visual areas. Our ERP measurements indicate that deprivation via strabismus affects both the early part of the evoked response that occurs before ICs are formed as well as the later IC-selective response. Importantly, these effects are found in the normal-acuity nonamblyopic eyes of strabismic amblyopes and in both eyes of strabismic patients without amblyopia. The nonamblyopic eyes of anisometropic amblyopes, by contrast, are normal. Our results indicate that beyond the well-known effects of strabismus on the development of normal binocularity, it also affects the early stages of monocular feature processing in an acuity-independent fashion.Over 50 y of research on experimental animal models has indicated that deprivation of normal visual experience during a developmental critical period perturbs both the structure and function of primary visual cortex (1–4). The animal models were developed to understand the underlying neural mechanisms of amblyopia, a common human developmental disorder of spatial vision associated with the presence of strabismus, anisometropia, or form deprivation during early life (5). Amblyopia is classically defined on the basis of poor visual acuity, but many other visual functions are known to be affected (6–8).The earliest experimental studies of visual deprivation focused on the effects of monocular lid suture, and these studies showed devastating effects on the ability of the deprived eye to drive neural responses, retain synaptic connections, and guide visual behavior (9–11). Later work studied less extreme forms of deprivation that are common in humans, such as the effects of strabismus (deviation of the pointing direction of the two eyes) (12, 13) or anisometropia (chronic optical blur) (14, 15). More recent studies (16, 17) have found that losses in cell responses in primary visual cortex appear to be insufficient to explain the magnitude of behaviorally measured deficits. Based on these results, a hypothesis has been put forward that these forms of deprivation have their primary effects in extrastriate cortex (16).Motivated by this idea, psychophysicists have sought evidence that extrastriate cortex is particularly impaired in human amblyopia. This work has used tasks whose execution is fundamentally limited by processing resources that single-cell physiology suggests are located in extrastriate cortex. As a second step, these studies have scaled stimuli based on visual acuity and compensated for contrast sensitivity losses to equate the output of early visual cortex from the amblyopic eye to that of normal-vision participants. Despite a nominal match at the level of early visual cortex outputs, patients with amblyopia still show deficits on illusory tilt perception (18), contour integration (19–23), global motion sensitivity (8, 24–28), object enumeration (29), and object tracking (7, 30). The impairments listed above have been interpreted to indicate that amblyopia may involve abnormalities in “higher-level” (e.g., extrastriate) neural processing that occur independent of any deficits in early processing stages (e.g., in striate cortex). A limitation of the existing psychophysical approaches has been the need to make an assumption that the stimulus scaling used to equate stimuli for visibility fully equilibrates the activity of early visual cortex. It would be preferable to take an approach that allows one to measure neural responses directly from both early and later stages of visual processing. Here we use event-related potentials (ERPs) and a stimulation paradigm that allow us to record responses from both early visual cortex and higher-level, extrastriate areas.Our approach is similar in spirit to existing psychophysical approaches: We use a stimulus configuration—illusory contours (ICs)—that previous single-unit studies have shown to be first extracted in extrastriate cortex (31–34). ICs, also referred to as subjective contours, render object borders that are perceptually vivid but that are created in the absence of luminance contrast or chrominance gradients (35). ICs have been widely used to study mechanisms of scene segmentation and grouping operations that are among the most fundamental tasks the visual system has to perform (36). ICs have garnered considerable interest because of their “inferential” nature—despite the lack of luminance edges, the visual system uses implicit configural cues to infer the presence of a contour. Finally, behavioral investigations in macaque suggest that IC perception is strongly dependent on higher visual areas, including V4 (37, 38) and inferotemporal (IT) cortex (39, 40).Instead of attempting to equate the visibility of stimuli in the amblyopic eye to that of normal control eyes, as has been typical practice in the study of amblyopia, we make a close analysis of the effects of deprivation that is based on ERP responses from the nonamblyopic eyes of patients with anisometropic or strabismic amblyopia. These eyes have normal visual acuity and normal or even supernormal contrast sensitivity (41), making the stimuli nominally equivisible without the need for scaling. We then measure evoked responses at early latencies before the time that IC selectivity arises to assess the integrity of early visual cortex, and compare these responses to those measured at longer latencies after robust IC selectivity has been established. Previous single-unit studies that have used ICs of the type used in the present study indicate that they are first extracted no later than V2 (31, 42, 43) or V4 (34). Given the difference in species and stimuli, we will refer in the following to evoked responses that lack IC sensitivity as having arisen in “early” visual cortex, rather than in specific visual areas. To further specify the site of deprivation effects, we also study a group of stereo-blind patients with strabismus who do not have amblyopia (normal visual acuity in each eye).A second goal of our study is to compare the effects of deprivation from unilateral blur (anisometropia) to that caused by strabismus. The human psychophysical literature has made a distinction in the pattern of visual loss associated with strabismus versus that associated with anisometropia (44). At least some of the differences in performance between these two types of deprivation can be explained on the level of residual stereopsis, which typically differs between these two populations (41). Whenever these two types of deprivation have been compared in terms of their effects on the monocular cell properties of V1, there has been little to differentiate the effects of the two types of deprivation (16, 45, 46). Unfortunately, there are relatively few studies of the effects of critical period deprivation on the cell-tuning properties in extrastriate cortex of any species (15, 17, 47), and there has been no comparison of the effects of strabismus vs. anisometropia in extrastriate cortex. The implication of the existing animal literature is that strabismus and anisometropia have comparable effects on early visual cortex and thus the divergence in their behavioral phenotype, as well as the major effects of deprivation, will lie in extrastriate cortex. Here we show that these two types of deprivation have differential effects very early in visual cortex, possibly as early as the transfer of information from V1 to V2.     

Development and aging of cortical thickness correspond to genetic organization patterns

There is a growing realization that early life influences have lasting impact on brain function and structure. Recent research has demonstrated that genetic relationships in adults can be used to parcellate the cortex into regions of maximal shared genetic influence, and a major hypothesis is that genetically programmed neurodevelopmental events cause a lasting impact on the organization of the cerebral cortex observable decades later. Here we tested how developmental and lifespan changes in cortical thickness fit the underlying genetic organizational principles of cortical thickness in a longitudinal sample of 974 participants between 4.1 and 88.5 y of age with a total of 1,633 scans, including 773 scans from children below 12 y. Genetic clustering of cortical thickness was based on an independent dataset of 406 adult twins. Developmental and adult age-related changes in cortical thickness followed closely the genetic organization of the cerebral cortex, with change rates varying as a function of genetic similarity between regions. Cortical regions with overlapping genetic architecture showed correlated developmental and adult age change trajectories and vice versa for regions with low genetic overlap. Thus, effects of genes on regional variations in cortical thickness in middle age can be traced to regional differences in neurodevelopmental change rates and extrapolated to further adult aging-related cortical thinning. This finding suggests that genetic factors contribute to cortical changes through life and calls for a lifespan perspective in research aimed at identifying the genetic and environmental determinants of cortical development and aging.There is a growing realization that events during development impact brain and cognition throughout the entire lifespan (1). For instance, the major portion of the relationship between cortical thickness and IQ in old age can be explained by childhood IQ (2), and genotype may explain a substantial part of the lifetime stability in intelligence (3). Effects of genes on the organization of the cortex have been shown in adults (4–6), but it is unknown whether and how regional differences in cortical development correspond to these regional genetic subdivisions.Although consensus has not been reached for the exact trajectories, cortical thickness as measured by MRI appears to decrease in childhood (7–12). The exact foundation for this thinning is not known, as MRI provides merely representations of the underlying neurobiology, and available histological data cannot with certainty be used to guide interpretations of MRI results. Although speculative, apparent thickness decrease may be grounded in factors such as synaptic pruning and intracortical myelination, although the link between established synaptic processes (13–15) and cortical thickness has not been empirically confirmed. After childhood, cortical thinning continues throughout the remainder of the lifespan, speculated to reflect neuronal shrinkage and reductions in number of spines and synapses (16), although similar to development, we lack data to support a direct connection between cortical thinning and specific neurobiological events.It has been demonstrated that genetic correlations between thickness in different surface locations can be used to parcellate the adult cortex into regions of maximal shared genetic influence (4). This result can be interpreted according to the hypothesis that genetically programmed neurodevelopmental events cause lasting impact on the organization of the cerebral cortex detectable decades later (4–6). Here we tested how developmental and lifespan changes fit the genetic organization of cortical thickness in a large longitudinal sample with 1,633 scans from 974 participants between 4.1 and 88.5 y of age, including 773 scans from children below 12 y Genetically based subdivisions of cortical thickness from an independent dataset of 406 twins (4) were applied to the data, yielding 12 separate regions under maximum control of shared genetic influences. We hypothesized that thickness in cortical regions with overlapping genetic architecture would show similar developmental and adult age change trajectories and dissimilar trajectories for regions with low genetic overlap.     

Prediction of the gait function using the nigrostriatal and corticoreticulospinal tracts of the affected hemisphere in a cerebral infarct: A diffusion tensor imaging study

Prognosis predictability of the nigrostriatal tract (NST) and corticoreticulospinal tract (CRT) of affected hemisphere at early stage for gait function at chronic stage were investigated using diffusion tensor tractography (DTT) in patients with a cerebral infarction.Thirty consecutive patients with middle cerebral artery (MCA) territory infarction were recruited. Functional ambulation category (FAC) was used to evaluate the gait function at chronic stage. Fractional anisotropy (FA) and tract volume (TV) of ipsilesional NST and ipsilesional CRT were determined to be DTT parameters at early stage.FAC score at chronic stage showed strong positive correlations with TVs of ipsilesional NST and ipsilesional CRT at early stage (ipsilesional NST R = 0.786; ipsilesional CRT R = 0.821; P < .05). According to regression model, FAC score at chronic stage was positively related to TVs of ipsilesional NST and ipsilesional CRT at early stage (Adjusted R² = 0.700, F = 34.905, P < .05). FAC score at chronic stage was associated more positively with TV of ipsilesional CRT (β = 0.532) than that of ipsilesional NST (β = 0.362).Ipsilesional NST and ipsilesional CRT at early stage had prognosis predictability for gait function at chronic stage in patients with an MCA infarction. Moreover, ipsilesional CRT had stronger predictability than ipsilesional NST.     

颅内电极脑电监测辅助下难治性枕叶癫痫的外科治疗

目的初步探索在颅内有创脑电监测下进行难治性枕叶癫痫外科治疗的效果。方法回顾性分析8例应用有创脑电监测的枕叶癫痫病例,所有病例均经过磁共振(MRI)、正电子发射断层扫描(PET)、头皮视频脑电监测(VEEG)等术前评估,初步判断癫痫起源在枕叶,再应用有创脑电监测,进一步明确致痫区的位置和范围,2期行致痫区手术切除。结果术后无死亡及严重并发症,其中1例视野缺损稍有加重。6例患者术后随访超过1 a,2例患者随访超过半年,其中6例术后无癫痫发作,2例发作次数明显减少。结论颅内电极长程脑电监测对于明确致痫区及视觉皮层、确定并精确切除致痫区具有重要意义,在其辅助下难治性枕叶癫痫的外科疗效提高,并发症减少。     

Recovery of an injured arcuate fasciculus via transcallosal fiber in a stroke patient: A case report

Rationale:We report on a patient whose arcuate fasciculus (AF) and corticobulbar tract (CBT) recovered following an infarct in the middle cerebral artery (MCA) territory, demonstrated on serial diffusion tensor tractography (DTT).Patient concerns:The patient showed moderate conduction aphasia on the Western Aphasia Battery with an aphasia quotient of 46.5‰ (spontaneous speech: 35.0‰, auditory comprehension: 36.0‰, and naming: 53.1‰) at 1 month after onset. His aphasia improved with an aphasia quotient of 49‰ (spontaneous speech: 71.0‰, auditory comprehension: 52.0‰, and naming: 59.0‰) at 10 months after onset.Diagnosis:A 44-year-old right-handed male patient presented with aphasia and quadriplegia, which occurred at the onset of an infarct in the left MCA territory.Intervention:Diffusion tensor imaging data were acquired twice (1 month and 10 months after onset).Outcomes:On one-month DTT, the discontinuation of the left AF and severe narrowing of the right CBT were observed. However, on ten-month DTT, the left AF was connected to the opposite AF by a new tract that passed through the splenium of corpus callosum, and the right CBT had become thicker.Lessons:We believe that our results suggest a recovery mechanism of injured AF and CBT in stroke patients.     

皮质下脑梗死患者初级运动皮质结构损伤和运动功能恢复的相关性研究

目的探讨脑梗死后结构损伤和功能代偿脑区的相关性,为阐述脑梗死后运动功能恢复的机制提供理论基础。方法选择运动功能恢复较好的慢性期单侧基底节区脑梗死患者28例(脑梗死组),健康体检者25例(对照组),功能MRI采用组块设计,进行患手虚握运动以及高分辨率结构像采集,采用统计参数图比较2组脑灰质体积和执行运动任务时脑激活的不同。结果与对照组比较,脑梗死组患侧半球M1区(感兴趣区1)及丘脑灰质体积减少。患手运动时,脑梗死组患侧半球M1区(感兴趣区2)及颞上回激活增强。感兴趣区1和感兴趣区2重叠,重叠区占灰质体积减少脑区(感兴趣区1)的21.9%。结论 M1结构损伤区及其周围正常脑区均参与运动功能的恢复,而与感觉功能有密切关系的M1区背侧的持续性激活增强可能对运动功能的恢复起更主要的作用。     

Functional specializations for music processing in the human newborn brain

In adults, specific neural systems with right-hemispheric weighting are necessary to process pitch, melody, and harmony as well as structure and meaning emerging from musical sequences. It is not known to what extent the specialization of these systems results from long-term exposure to music or from neurobiological constraints. One way to address this question is to examine how these systems function at birth, when auditory experience is minimal. We used functional MRI to measure brain activity in 1- to 3-day-old newborns while they heard excerpts of Western tonal music and altered versions of the same excerpts. Altered versions either included changes of the tonal key or were permanently dissonant. Music evoked predominantly right-hemispheric activations in primary and higher order auditory cortex. During presentation of the altered excerpts, hemodynamic responses were significantly reduced in the rig1ht auditory cortex, and activations emerged in the left inferior frontal cortex and limbic structures. These results demonstrate that the infant brain shows a hemispheric specialization in processing music as early as the first postnatal hours. Results also indicate that the neural architecture underlying music processing in newborns is sensitive to changes in tonal key as well as to differences in consonance and dissonance.     

From the Cover: Visually evoked activity in cortical cells imaged in freely moving animals

We describe a miniaturized head-mounted multiphoton microscope and its use for recording Ca²⁺ transients from the somata of layer 2/3 neurons in the visual cortex of awake, freely moving rats. Images contained up to 20 neurons and were stable enough to record continuously for >5 min per trial and 20 trials per imaging session, even as the animal was running at velocities of up to 0.6 m/s. Neuronal Ca²⁺ transients were readily detected, and responses to various static visual stimuli were observed during free movement on a running track. Neuronal activity was sparse and increased when the animal swept its gaze across a visual stimulus. Neurons showing preferential activation by specific stimuli were observed in freely moving animals. These results demonstrate that the multiphoton fiberscope is suitable for functional imaging in awake and freely moving animals.     

Functional brain imaging of episodic memory decline in ageing

The episodic long‐term memory system supports remembering of events. It is considered to be the most age‐sensitive system, with an average onset of decline around 60 years of age. However, there is marked interindividual variability, such that some individuals show faster than average change and others show no or very little change. This variability may be related to the risk of developing dementia, with elevated risk for individuals with accelerated episodic memory decline. Brain imaging with functional magnetic resonance imaging (MRI) of blood oxygen level‐dependent (BOLD) signalling or positron emission tomography (PET) has been used to reveal the brain bases of declining episodic memory in ageing. Several studies have demonstrated a link between age‐related episodic memory decline and the hippocampus during active mnemonic processing, which is further supported by studies of hippocampal functional connectivity in the resting state. The hippocampus interacts with anterior and posterior neocortical regions to support episodic memory, and alterations in hippocampus–neocortex connectivity have been shown to contribute to impaired episodic memory. Multimodal MRI studies and more recently hybrid MRI/PET studies allow consideration of various factors that can influence the association between the hippocampal BOLD signal and memory performance. These include neurovascular factors, grey and white matter structural alterations, dopaminergic neurotransmission, amyloid‐Β and glucose metabolism. Knowledge about the brain bases of episodic memory decline can guide interventions to strengthen memory in older adults, particularly in those with an elevated risk of developing dementia, with promising results for combinations of cognitive and physical stimulation.     

Global impairment and therapeutic restoration of visual plasticity mechanisms after a localized cortical stroke

We tested the influence of a photothrombotic lesion in somatosensory cortex on plasticity in the mouse visual system and the efficacy of anti-inflammatory treatment to rescue compromised learning. To challenge plasticity mechanisms, we induced monocular deprivation (MD) in 3-mo-old mice. In control animals, MD induced an increase of visual acuity of the open eye and an ocular dominance (OD) shift towards this eye. In contrast, after photothrombosis, there was neither an enhancement of visual acuity nor an OD-shift. However, OD-plasticity was present in the hemisphere contralateral to the lesion. Anti-inflammatory treatment restored sensory learning but not OD-plasticity, as did a 2-wk delay between photothrombosis and MD. We conclude that (i) both sensory learning and cortical plasticity are compromised in the surround of a cortical lesion; (ii) transient inflammation is responsible for impaired sensory learning, suggesting anti-inflammatory treatment as a useful adjuvant therapy to support rehabilitation following stroke; and (iii) OD-plasticity cannot be conceptualized solely as a local process because nonlocal influences are more important than previously assumed.     

Microstimulation reveals specialized subregions for different complex movements in posterior parietal cortex of prosimian galagos

Posterior parietal cortex of prosimian galagos consists of a caudal half characterized by connections with visual cortex and a rostral half connected with motor, premotor, and visuomotor areas of frontal cortex. When 500-ms trains of electrical pulses were used to stimulate microelectrode sites throughout posterior parietal cortex, movements were elicited only from the rostral half. The movement zone reflected an overall pattern of somatotopy, from eye and face movements most ventrally to hindlimb movements most dorsally. In addition, subregions or zones of this movement cortex seemed to be devoted to components of different, ethologically significant behaviors. Thus, microstimulation within separate zones of cortex elicited reaching, hand-to-mouth, defensive, or aggressive movements. The finding of similar classes of elicited movement patterns from frontal and more recently intraparietal cortex of macaques suggests that multiareal circuits for biologically significant behaviors are components of all primate brains and that these circuits can be activated by long trains of current pulses at rostral locations in posterior parietal cortex.