脑内源信号光学成像术:猫视皮质方位功能柱的活体显示

脑内源信号光学成像术是目前为止空间分辨率最高的一种活体脑成像技术,它为大范围皮质的功能构筑研究提供了有力工具.本文介绍了应用这一技术显示活体猫视皮质的方位功能柱的方法,此方法基本上也适用于其他皮质的功能构筑研究.     

左旋多巴甲酯可增加斜视性弱视模型猫视皮质17区神经生长因子的表达

实验以处于发育敏感期的猫建立斜视性弱视动物模型,比较左旋多巴甲酯及左旋多巴对斜视性弱视猫视皮质17区神经生长因子表达的影响。图形视觉诱发电位结果和免疫组织化学检测结果显示,左旋多巴及左旋多巴甲酯均能缩短斜视性弱视模型猫P100波潜时,增大P100波幅,还能使其视皮质各层的内源性神经生长因子免疫阳性细胞数量增加,但左旋多巴甲酯的治疗效果优于左旋多巴。     

脑磁图定位皮质运动区与术中皮质电刺激运动诱发电位的对照研究

目的评价脑磁图（MEG）术前定位初级运动皮质（M1）的准确性。方法选取顺序入院的中央区胶质瘤26例,术前均运用MEG定位皮质运动区,与MRI导航影像融合,在神经导航下定位MEG激活区。术中对MEG成功定位的病例行直接皮质电刺激（DCES）,比较两种技术的吻合度。结果因病人不能配合,MEG定位失败2例,余24例均定位成功,每例激活区1～5个。DCES成功监测24例,所有选择的DCES靶点共41个,阳性靶点24个,1个/例。以所有的41个靶点分析,MEG定位M1区与DCES定位的吻合率为58.5%;而以第1组病灶侧M1区和第2组病灶侧中央区的MEG激活区中27个靶点分析,两者吻合率为88.9%;仅以第1组M1区的MEG激活区中17个靶点分析,两者吻合率为100%。结论 MEG可以灵敏而可靠地定位M1区,可用于中央区胶质瘤病人术前手术规划。     

高分辨率OCT成像在脑胶质瘤术中定性诊断与边界定位的应用研究

目的 探究高分辨率光学相干断层扫描(OCT)成像在脑胶质瘤术中定性诊断与边界定位的应用价值.方法 选取河北医科大学第二医院脑胶质瘤术中切除的肿瘤组织32例作为研究对象,另选取术中造瘘切除的正常脑组织6例作为对照对象,均行高分辨率OCT成像检查,比较脑胶质瘤组织、正常脑组织(白质、皮质)的衰减系数、前向交叉散射系数,评价...     

Comparative analysis of orientation maps in areas 17 and 18 of the cat primary visual cortex following adaptation

Object orientations in the visual field are columned into specific orientation domains in the primary visual cortex [area 17 (A17) and area 18 (A18)] of cats. At the single‐cell level, adapting A17 neurons to a non‐preferred orientation (adaptor) shifts their preferred orientation either towards the adaptor (attractive shift) or away from it (repulsive shift). As A17 and A18 are reciprocally connected, we sought to determine how changes in preferred orientations in A18 neurons are correlated with changes recorded in A17 anesthetised cats. To this end, we simultaneously traced populations of neurons in A17 and A18, using intrinsic optical imaging, before and after long (12 min) and short (3 min) adaptations. The comparison of A17 and A18 maps pre‐adaptation and post‐adaptation showed that variance in shift amplitudes is greater in A18 than A17 for short adaptations. Our results indicate a rapid reconfiguration of functional maps that may spread to many cortical areas.     

Functional segregation of plural regions representing cardinal contours in cat primary visual cortex

Our previous data based on an imaging study suggested that, in cat area 17, the representations of cardinal orientations overlap less than the representation of their nearby angles. The purpose of this study was to further investigate the underlying single-cell properties. Optical imaging was performed first to map the cortical regions corresponding to the four principal contours, the two cardinals and the two obliques. The cortical region activated by a principal orientation but not by the +10 degrees or -10 degrees neighbouring angles, namely the area with optically relative independent orientation selectivity (RIOS), was mapped together with the regions that overlapped with the +10 degrees and/or -10 degrees neighbouring angles (non-RIOS). Electrode penetrations were targeted to the RIOS and non-RIOS regions in each of the four orientations. A comparison between the RIOS and the non-RIOS regions documented a significantly higher percentage of cells with the orientation preference of the cardinal orientations in the cardinal RIOS region than that seen in the other regions. Additionally, the difference in the tuning width of cells between the RIOS and non-RIOS in the cardinal region was significantly larger than the difference between the RIOS and non-RIOS in the oblique region. The cells in the cardinal RIOS region were tuned more sharply and the cells in cardinal non-RIOS region more broadly than the oblique RIOS and/or the non-RIOS region, which showed no significant difference. These data strongly suggest the existence of functional segregation in the region corresponding to the cardinal contours.     

Surround modulation in cortical orientation map revealed by optical imaging and its dependency on receptive field eccentricity

Optical imaging was used to investigate the difference in surround modulation on orientation map related to receptive field eccentricity in cat visual cortex. Presentation of center–surround stimuli at the center of gaze resulted in no clear surround modulation; however, significant modulation was observed in its corresponding cortical area when the center–surround stimuli were presented at 10° eccentricity in more peripheral parts of the visual field. Modulation was observed both in the response magnitude and in the spatial pattern of the response. Surround orientation perpendicular to the orientation of a center patch grating showed the largest modulation in the response magnitude. The modulation became weaker as the orientation difference between the center and surround gratings became smaller. Regardless of the orientations for the central patch gratings, a similar response spatial pattern was observed in the cortical region where the underlying cells had their receptive fields covering the central patch, if the stimuli were with the same surround gratings. These properties support the notion of a relative specialization for visual information processing in peripheral representations of cortical areas.     

Organization of direction preferences in cat visual cortex

Single unit recordings were made from the visual cortex of 5 adult cats. Visual stimuli were used to determine the stimulus orientation and direction of movement preferred by cortical cells. Analysis of the sequence of neurons recorded along each electrode penetration and their direction preferences indicates that neurons preferring similar directions of movement are clustered together in the cortex.     

Meridional variations in the line orientation discrimination of the cat

Cat's differential orientation thresholds were measured with single lines presented in succession. Differential orientation thresholds measured at horizontal or vertical orientations were smaller (median 2.9 degrees) than those measured at oblique orientation (median 4.7 degrees). Replications of the experiments showed that the oblique effect was stable over a period of 2 years. Using the same behavioral methods grating acuity was measured and did not show an oblique effect. These behavioral observations are compared with the physiological data on orientation specificity of area 17 cells. This comparison suggests that the most likely explanation of the meridional variation in orientation discrimination is the meridional variation in orientation preference of area 17 S cells.     

Noninvasive optical imaging in the visual cortex in young infants

During the developmental stage, the brain undergoes anatomic, functional, and metabolic changes necessary to support the complex adaptive behavior of a mature individual. Estimation of developmental changes occurring in different regions of the brain would provide a means of relating various behavioral phenomena to maturation-specific brain structures, thereby providing useful information on structure-function relationships in both normal and disease states. We used multichannel near-infrared spectroscopy (MNIRS), a new noninvasive imaging technique for revealing the course of neural activity in selected brain regions, to monitor the activities of the visual cortex as mirrored by hemodynamic responses in infants subjected to photostimulation during natural sleep. In the infants, oxyhemoglobin and total hemoglobin decreased and deoxyhemoglobin increased in the visual cortex with photostimulation. This pattern of responses was different from the response pattern in adults reported previously. The different patterns of responses to photostimulation in the visual cortices of infants and adults might reflect developmental and behavioral differences. It may reflect a different functional organization of the visual cortex in infants or ongoing retinal development. Our results demonstrated that regional hemodynamic change could be detected in a small area around the visual cortex. MNIRS offers considerable potential for research and noninvasive clinical applications.     

Principal components analysis of cells in cat visual cortex

Cortical cells differ along many dimensions, and statistical techniques are needed to study the relationships among them. We have used principal components analysis to study variation within a population of cells in the visual cortex of the cat. This procedure transforms the data which may then be projected onto a small number of independent axes. The axes are hierarchically ordered in terms of the sample variance they account for so that subsequent components account for decreasing proportions of the total sample variance.Four principal components (PCs) were identified by the analysis. The contributing variables on these components were respectively: (1) cutoff velocity, peak response, receptive field area and spontaneous activity; (2) tuning width, orientation selectivity, occular dominance ratio and obliquity; (3) directionality ratio, monocularity and vvariability; and (4) width to length ratio, variability and sideband ratio. We hypothesize that each of these components identifies a physiologically important feature of cortical organization. PC₁ and PC₄ describe those relationships among variables that have been used previously by other workers to classify cells in the visual cortex of the cat. Specifically, PC₁ is highly correlated with those variables associated with type of afferent input and PC₄ is highly correlated with those variables that differentiate simple cells from complex cells. PC₂ and PC₃, however, are highly correlated with variables that have not been used in classiying cells. Our results demonstrate that: (1) each of two major classification schemes (simple/complex and classification by afferent input) describe important differences among neurons in the cat's visual cortex and both must be incorporated into a comprehensive system for classifying cells in the cat's visual cortex; and (2) these two schemes when combined do not account for all the major differences among neurons in cat visual cortex, and at least two additional components are required: one related to orientation selectivity and dominance by the ipsilateral eye, and another related to directional selectivity and the degree of binocular interaction.     

Differential effects of neurotrophins on ocular dominance plasticity in developing and adult cat visual cortex

In the present study we examine the influence of neurotrophins on experience-dependent synaptic rearrangement in developing and adult visual cortex. Brain-derived neurotrophic factor (BDNF) or nerve growth factor (NGF) was continuously infused into cortical area 18, and the functional architecture of the cortex was examined by use of optical and electrophysiological recording techniques. In kittens, BDNF infusion during monocular deprivation (MD) reversed the normally occurring ocular dominance (OD) shift towards the non-deprived eye so that the deprived eye dominated the BDNF-treated cortex after MD. Under conditions of equal activation of thalamocortical synapses, i.e. when animals were either subject to binocular deprivation (BD) or reared without deprivation, BDNF infusion did not disrupt binocularity of cortical units, but reversed the natural OD bias towards the contralateral eye in favour of the ipsilateral eye. In addition, BDNF treatment in kittens led to a loss of the orientation selectivity of cortical units irrespective of rearing conditions. In adult animals, BDNF influenced neither OD distributions nor orientation selectivity. The effect of NGF was markedly different. It was ineffective in kittens but in adult animals it caused a shift of OD towards the deprived eye when MD was combined with NGF infusion. However, in this case orientation selectivity was preserved. Thus, both neurotrophins have profound activity- and age-dependent effects on the functional architecture of the visual cortex. Moreover, our results indicate that simple substitution of neurotrophins in excess is unlikely to compensate for deprivation effects by preserving or restoring the normal functional architecture of the cortex.     

Orientation topography of layer 4 lateral networks revealed by optical imaging in cat visual cortex (area 18)

The functional specificity of corticocortical connections with respect to the topography of orientation selectivity was studied by optical imaging of intrinsic signals and bulk injections of fluorescent latex beads (green and red) and biocytin into layer 4. The distributions of retrogradely labelled cells and anterogradely labelled axon terminals were histologically reconstructed from all cortical laminae, and the resulting anatomical maps compared with the optically imaged functional maps. Layer 4 injections produced extensive horizontal labelling up to 2-3 mm from the injection centres albeit without the clear patchy pattern described after layer 2/3 injections (Gilbert & Wiesel 1989, J. Neurosci., 9, 2432-2442; Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618). The functional (orientation) distribution of the labelled projections was analysed according to laminar location and lateral spread. With regard to the former, no major difference in the orientation topography between supragranular- (upper tier), granular- (middle tier) and infragranular (lower tier) layers was seen. Laterally, proximal and distal projections were distinguished and further dissected into three orientation categories, iso- (+/- 30 degrees ), oblique- (+/- 30-60 degrees ) and cross-orientations (+/- 60-90 degrees ) with respect to the orientation preference at the injection sites. The majority of distal connections (retrograde and anterograde) was equally distributed across orientations (35.4% iso-, 33.7% oblique-, and 30.9% cross-orientations) that are equivalent with a preponderance to dissimilar orientations (oblique- and cross-orientations, 64.6%). In one case, distal excitatory and inhibitory connections could be morphologically distinguished. For both categories, a marked bias to dissimilar orientations was found (excitatory, 63.7%; inhibitory, 86.6%). Taken together, these results suggest that the long-range layer 4 circuitry has a different functional role from that of the iso-orientation biased (52.9%, Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618) layer 2/3 circuitry, and is perhaps involved in feature difference-based mechanisms, e.g. figure ground segregation.