基于三维建模的猫内侧膝状体与听皮层的投射研究

目的研究猫内侧膝状体(medial geniculate body,MGB)的立体定位与主要亚核团的三维可视化及其与听皮层(auditory cortex,AC)的神经投射。方法在细胞构筑及采用辣根过氧化物酶(Horseradish Peroxidase,HRP)、生物素葡聚糖胺(biotinylated dextran amine,BDA)进行神经追踪基础上,建立猫内侧膝状体及听皮层冠状切片的二维数据库,通过软件Amira实现可视化及三维建模。结果1.猫内侧膝状体腹侧群(MGBv)、背侧群(MGBd)以及内侧群(MGBm)三个主要亚核团的重建模型真实、精确,再现了猫右脑半球内MGB各亚核团的自然形态及毗邻。2.内侧膝状体各亚核团的构成方式、听皮层的层状分布模式、广义听皮层内部各亚区之间的配布模式之间存在着相对应的组构格局。结论细胞构筑、神经示踪、组织化学染色和数字人图像处理技术相结合,实现了内侧膝状体主要亚核团的三维重建,对听觉通路的相关研究和小核团的数字解剖学研究具有重要意义。     

髋臼区域皮质骨厚度分布特征的三维图像测量*☆

背景：课题组前期研究建立了采用正常人体的CT数据构筑三维模型研究皮质骨厚度的空间分布的方法。 目的：根据髋骨皮质骨三维厚度分布规律对髋臼区域的皮质骨厚度进行分区。 方法：使用Mimics对8名健康志愿者髋骨CT图像进行分割提取皮质骨并建立几何模型。以A平台提供的二次开发语言PCL编写皮质骨厚度测量的新算法。获得厚度数据后根据各厚度范围皮质骨分布面积的大小,采用聚类分析的方法对测得的厚度范围进行分组。 结果与结论：髋骨皮质骨厚度介于0.44~4.00 mm,采用聚类分析的方法发现可分为0.44~1.133 mm、1.133~1.826 mm及1.826~4.00 mm 3组,按照这3组厚度范围对髋骨模型进行渲染后发现整个髋骨的皮质骨的较厚部位可分为明显的三组皮质骨束,第1组沿弓状线延伸至耻骨联合,第2组从臼顶延伸到髂结节,第3组分布在坐骨大切迹上下。说明在髋臼区域皮质骨较厚的部位可大致分为3组,其部位与应力集中点点基本吻合。     

定量CT测定锁骨远端骨密度分区指导肩锁关节脱位重建的价值

背景：肩锁关节脱位喙锁韧带重建在锁骨侧骨隧道的最佳位置尚未达成共识，且术后会发生锁骨侧骨隧道扩大、骨溶解、锁骨骨折、内固定失效等并发症。骨密度在内植物固定强度及稳定性上起重要作用，锁骨远端骨密度的区域差异在肩锁关节脱位修复重建中不应被忽视，目前临床上尚无人体有关锁骨远端骨密度的定量研究。目的：通过定量CT测量锁骨远端不同区域骨密度的大小，为外科医生修复重建喙锁韧带提供参考。方法：对2022年10-12月在安徽医科大学附属阜阳人民医院(阜阳市人民医院)行定量CT检查的101例患者1 616份亚分区进行锁骨远端骨密度测量。对于每个定量CT样本，首先由内侧向外侧划分锁骨远端为以下4个区域，即锥状结节区(A区)、结节间区(B区)、斜方嵴区(C区)以及锁骨远端区(D区)，再将每个区域分为前半部分和后半部分确定8个亚分区，在亚分区中设置半自动感兴趣区(ROI A1、A2、B1、B2、C1、C2、D1、D2)，将每个定量CT扫描图像传输至QCT pro分析工作站，对锁骨远端感兴趣区松质骨骨密度进行测量，测量时注意避开锁骨骨皮质。结果与结论：(1)不同侧肩部骨密度比较，差异无显著性意义(P> 0...     

猫主要过敏原Fel d 1的T细胞抗原表位分析及三维结构模拟

目的:预测猫主要过敏原Fel d 1与MHC Ⅰ、MHCⅡ类分子的结合力获得T细胞优势抗原表位,并模拟Fel d 1的三维结构,为猫主要过敏原的改造及其临床研究等提供依据.方法:从Uniprot数据库中得到猫主要过敏原Fel d 1的氨基酸序列,通过在线软件NetMHCⅡ2.2对Fel d 1氨基酸序列进行MHCⅡ抗原表位分析,使用软件SYFPEITHI分析MHC Ⅰ的抗原表位,再通过在线软件Swiss-Model预测Feld1的三维结构,以Ramachandran图评估三维结构的稳定性.结果:运用生物学软件分析得到Fel d 1上两个高值MHCⅡ抗原表位区域分别为22～43、80～95,MHC Ⅰ抗原表位优势区为17～30、56～84、91 ～103.Ramachandran图显示Feld 1的空间构象稳定.结论:本研究有助于确定Fel d 1的T细胞优势抗原表位及其三维结构模型,为Fel d 1抗原性改造提供理论依据,及将来的临床研究奠定基础.     

三四岁儿童基底核团的三维形态学特点

文题释义：脑功能：前额叶皮质,被认为是认知的主要区域,与皮质下的脑区,特别是基底核有很强的联系,基底核主要参与运动过程。皮质负责启动认知、运动和行为指令,基底核通过正反馈执行这些指令。 大脑基底核：是埋藏在两侧大脑半球深部的一些灰质团块,是组成锥体外系的主要结构。它主要包括尾状核、豆状核(壳核和苍白球)、屏状核以及杏仁复合体。 背景：国内外对于成人大脑基底核团的研究较多,多借助影像学手段测量,而关于三四岁儿童基底核团形态学三维重建与测量甚少。 目的：建立三四岁儿童基底核团的三维立体模式,与其他年龄段进行比较,为探讨基底核团的神经发育提供形态学依据。 方法：选取三四岁儿童尸体15例,薄层切割基底核团,并完成其主要结构精确分割的图像数据集;分析各断面标本主要结构的横断面,在特定断面测量相关结构的径线和角度,比较侧别间差异;对原始数据进行重新采样,建立基底核团三维空间坐标系。测量基底核团主要结构的形态大小,明确解剖标识,量化空间信息,建立模型和公共参考系统;三维立体显示基底核团结构,对于各个结构赋以不同颜色,清晰显示其各结构间边界,并行任意角度旋转切割,观测其内部结构。研究方案的实施符合内蒙古医科大学的相关伦理要求。标本均为儿童监护人自愿捐献并签署“知情同意书”。 结果与结论：①获得儿童标本基底核团的连续横断面图像信息,通过重建获得其三维模型,重建结构不仅可显示其基底核团,测量基底核团体积、经线相关参数,侧别间差异无统计学意义;②所得三维重建结构可行任意角度、不同速度旋转,并可行相应的缩放及透明处理,使重建结构图像更加真实和逼真;③基于体绘制重建三四岁儿童基底核团为神经立体定向导航手术及癫痫等诊治提供形态学依据。 ORCID: 0000-0001-5877-8358(许阳阳);0000-0001-7716-9515(高尚) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

白介素-1βmRNA在缺血侧大脑半球不同区域表达的比较

目的：比较缺血侧大脑半球尾壳核、视前区和顶叶皮质白介素－１βｍＲＮＡ表达的差异,探讨脑不同区域对缺血敏感性的病理机制。方法：运用原位杂交技术对３０只ＳＤ大鼠进行了研究。结果：缺血侧大脑半球尾壳核、视前区和顶叶皮质微血管内皮细胞和单核／巨噬细胞显示白介素－１βｍＲＮＡ的强杂交信号,尾壳核杂交信号较视前区和顶叶皮质出现早而强。顶叶皮质的白介素－１βｍＲＮＡ阳性信号的高峰也明显迟于尾壳核。结论：白介素－     

新型骶髂关节内固定系统的三维仿真与对比验证

目的 建立使用新型的骶髂关节解剖型棒-板内固定系统（SABP）对骶髂关节骨折脱位 进行固定的三维有限元模型,并与骶髂关节螺钉、和前路重建钢板固定进行对比,验证 和分析其力学性能。 方法 根据CT扫描数据,采用专门的流线型生物力学有限元网格划 分器,建立完整骨盆三维有限元模型。去掉模型一侧的骶髂关节韧带群模拟骨折脱位, 使用新型的SABP内固定系统进行固定模拟,同时分别使用骶髂关节螺钉（SS）和前路重 建钢板固定（SP）建立对比模型,进行加载计算,分析受力情况。 结果 SABP 固定的 最大位移值比 SS固定减小约40%,比 SP固定减小约42%。与对照组相比,SABP 固定模 型中,在主要传承负载区域的最大Stress 值均为最小：在损侧髋皮质骨、和损侧髋软 骨区域, 比SS固定减小约 33%-70%;在骶皮质骨、和损侧髋皮质骨区域,比SP固定减 约 60%-75%。 结论 新型骶髂关节解剖型棒-板内固定系统的固定形式更趋合理,固定 结构更趋稳定,为骨盆骨折的治疗增加了一种更有效的新方法。     

猫视神经连续切片的计算机三维重建

目的制备猫视神经的连续切片,选择合适的染色方法 ,寻找合适的配准方法 ,经图像采集及初步处理后利用计算机的三维重建技术,获得可视化的猫视神经三维结构。方法利用石蜡切片技术的制备猫视神经连续切片,采用特殊的神经三色染色法进行切片染色。利用数码显微镜及Motic Images Advanced 3.0和Motic Images Assembly 1.0软件对连续的猫视神经石蜡切片进行拍照,获得猫视神经连续切片的原始图像,将原始图像在GIMP软件中经过调整亮度对比度、初步图像配准、提取神经束膜图像信息后在Amira软件下,经过计算机在手工配准的基础上进一步自动配准,把二维的切片图像重建成三维的可视化图像。结果实验所得经三色染色的连续切片的原始图像上神经束膜能较好的与周围的组织区分;利用Amira三维重建软件,重建得到猫视神经三维结构图像,重建后的猫视神经结构三维图像可进行任意的切割、旋转、回复、拍照等操作。结论实验证明在不利用标志线的条件下,通过制备视神经连续切片,经过染色拍照,手工图像配准后利用计算机自动配准技术对视神经进行三维重建是完全可行的。     

活动平台单髁假体的三维有限元模型建立及受力分析

目的为活动平台膝关节单髁置换有限元分析提供一种参数化联合建模方法并分析其受力变化。方法获取1例成年男性正常膝关节的膝部CT扫描,利用Mimics 13.1软件重建膝关节三维模型,通过参数化软件Rhinoceros5.0设计与骨性模型相匹配的单髁假体,导入Mimics 13.1建立膝关节单髁置换三维模型,然后通过Abaqus6.10建立活动平台膝关节单髁置换三维有限元模型,并进行有限元分析皮质骨、松质骨的应力。结果参数化联合建模法效率高,所建模型形态逼真,精确度高,假体置换前后胫骨侧皮质骨应力变化基本一致,置换后胫骨侧松质骨受力主要在假体槽部。结论参数化联合建模法为膝关节单髁置换的生物力学研究提供了有效模型和新的研究思路,在单髁置换治疗膝关节病的临床和科研中将有广泛的应用前景。     

网膜囊与毗邻结构空间关系的三维可视化研究

目的 运用三维可视化技术深入了解网膜囊的解剖特征,以弥补厚层断面解剖与CT图像无法清晰显示网膜囊及其毗邻结构的空间关系的不足。方法 从2号中国可视人数据库（CVH2）获取上腹部图像数据,对网膜囊各隐窝及其毗邻结构进行数据分割,三维可视化重建和多平面重建后进行两种重建图像的整合,并在断层与三维多角度观察网膜囊各隐窝与毗邻结构的空间关系。在53例肝硬化伴大量腹水患者的CT多平面重建图像上观察上述空间关系,并判断上、下隐窝通连情况。结果 网膜囊由上隐窝、前庭部、下隐窝和脾隐窝组成。网膜囊大孔是上、下隐窝的分界标志,也是上、下隐窝通连的唯一路径,CT图像显示其通连方式分为通连和不通连两型,36例（67.9%）患者的CT图像上可见上、下隐窝直接通连,17例（32.1%）患者不通连。网膜孔右侧正对门腔间隙,该间隙最小前后径为4.5 mm。三维图像显示胃裸区位于上隐窝、下隐窝和脾隐窝之间。脾隐窝被左侧的脾裸区包饶。结论 本研究运用CVH2图像可视化技术呈现了网膜囊及其与毗邻结构的空间关系,这将有助于提高网膜囊区域病变的鉴别诊断和解剖定位的准确性,从而降低网膜囊区病变的误诊率。     

Anatomic subdivisions in human temporal cortical neuronal activity related to recent verbal memory.

We identified functional anatomical subdivisions of human lateral and basal temporal cortex related to recent verbal memory for object names, text and auditory words. Extracellular neuronal activity was recorded during memory encoding compared to identification, during encoding, storage or recall retrieval stages of the memory task, during recognition memory, and during implicit memory as measured by repetition priming. Changes in frequency of activity during encoding were recorded from most neurons. In lateral temporal cortex, these encoding changes in the dominant hemisphere were more likely to be polymodal, whereas those in nondominant hemisphere were unimodal. There was substantial separation of neurons with changes in other aspects of memory, defining additional subdivisions. Inferior lateral and basal cortex were related to memory stages, and superior-posterior lateral cortex was related to implicit and recognition memory.     

The cytoarchitecture of the inferior colliculus revisited: a common organization of the lateral cortex in rat and cat

The inferior colliculus (IC) is the major component of the auditory midbrain and contains three major subdivisions: a central nucleus, a dorsal cortex, and a lateral cortex (LC). Discrepancies in the nomenclature and parcellation of the LC in the rat and cat seem to imply different, species-specific functions for this region. To establish a comparable parcellation of the LC for both rat and cat, we investigated its histochemistry and inputs. In both species, the deep lateral cortex is marked by a transition between the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) rich superficial cortex and a cytochrome oxidase (CO) rich central nucleus. In both species, focal injections of anterograde tracers in the cochlear nucleus at sites of known best frequency produced bands of labeled inputs in two different subdivisions of the IC. A medial band of axons terminated in the central nucleus, while shorter bands were located laterally and oriented nearly perpendicularly to the medial bands. In the rat, these lateral bands were located in the third, deepest layer of the lateral (external) cortex. In the cat, the bands were located in a region that was previously ascribed to the central nucleus, but now considered to belong to the third, deepest layer of the LC, the ventrolateral nucleus. In both species, the LC inputs had a tonotopic organization. In view of this parallel organization, we propose a common parcellation of the IC for rat and cat with a new nomenclature. The deep layer of the LC, previously referred to as layer 3 in the rat, is designated as the 'ventrolateral nucleus' of the LC, making it clear that this region is thought to be homologous with the ventrolateral nucleus in the cat. The similar organization of the LC implies that this subdivision of the IC has similar functions in cats and rats.     

Cytoarchitecture of the medial geniculate body and thalamic projections to the auditory cortex in the rufous horseshoe bat (Rhinolophus rouxi). I. Temporal fields

The auditory cortex in echolocating bats is one of the best studied in mammals, yet the projections of the thalamus to the different auditory cortical fields have not been systematically analyzed in any bat species. The data of the present study were collected as part of a combined investigation of physiological properties, neuroarchitecture, and chemoarchitecture as well as connectivity of cortical fields in Rhinolophus in order to establish a neuroanatomically and functionally coherent view of the auditory cortex in the horseshoe bat. This paper first describes the neuroanatomic parcellation of the medial geniculate body and then concentrates on the afferent thalamic connections with auditory cortical fields of the temporal region. Deposits of horseradish peroxidase and wheatgerm-agglutinated horseradish peroxidase were made into neurophysiologically characterized locations of temporal auditory cortical fields; i.e., the tonotopically organized primary auditory cortex, a ventral field, and a temporal subdivision of a posterior dorsal field. A clear topographic relationship between thalamic subdivisions and specific cortical areas is demonstrated. The primary auditory cortex receives topographically organized input from the central ventral medial geniculate body. The projection patterns to the temporal subdivision of the posterior dorsal field suggest that it is a "core" field, similar to the posterior fields in the cat. Projections to the ventral field arise primarily from border regions of the ventral medial geniculate body. On the whole, the organization of the medial geniculate body projections to the temporal auditory cortex is quite similar to that described in other mammals, including cat and monkey.     

Cytoarchitecture of the medial geniculate body and thalamic projections to the auditory cortex in the rufous horseshoe bat (<Emphasis Type="Italic">Rhinolophus rouxi)</Emphasis>

The auditory cortex in echolocating bats is one of the best studied in mammals, yet the projections of the thalamus to the different auditory cortical fields have not been systematically analyzed in any bat species. The data of the present study were collected as part of a combined investigation of physiological properties, neuroarchitecture, and chemoarchitecture as well as connectivity of cortical fields in Rhinolophus in order to establish a neuroanatomically and functionally coherent view of the auditory cortex in the horseshoe bat. This paper first describes the neuroanatomic parcellation of the medial geniculate body and then concentrates on the afferent thalamic connections with auditory cortical fields of the temporal region. Deposits of horseradish peroxidase and wheatgerm-agglutinated horseradish peroxidase were made into neurophysiologically characterized locations of temporal auditory cortical fields; i.e., the tonotopically organized primary auditory cortex, a ventral field, and a temporal subdivision of a posterior dorsal field. A clear topographic relationship between thalamic subdivisions and specific cortical areas is demonstrated. The primary auditory cortex receives topographically organized input from the central ventral medial geniculate body. The projection patterns to the temporal subdivision of the posterior dorsal field suggest that it is a “core” field, similar to the posterior fields in the cat. Projections to the ventral field arise primarily from border regions of the ventral medial geniculate body. On the whole, the organization of the medial geniculate body projections to the temporal auditory cortex is quite similar to that described in other mammals, including cat and monkey.     

Pathological and experimentally induced blindness induces auditory activity in the cat primary visual cortex

Early blindness in humans and experimental visual deprivation in animal models are known to induce compensatory somatosensory and/or auditory activation of the visual cortex. An abnormal hydrocephalic cat with extreme malformation of the visual system, born in our breeding colony, rendered a good model system for investigating possible cross-modal compensation in such a pathological case. For comparison, we used normal and neonatally enucleated cats. When introduced to a novel environment, the abnormal cat behaved as if it was completely blind, yet it responded normally to auditory stimuli. As anticipated, single cells in the visual cortex of normal cats responded to visual, but not to auditory stimuli. In the visual cortex of enucleated cats, flashes of light did not elicit field-evoked potentials or single-unit responses. However, several cells did respond to various auditory stimuli. In the remnant visual cortex of the abnormal cat, auditory stimuli evoked field potentials and single-cell responses. Unexpectedly, however, unlike the enucleated cats, in the abnormal cat, flashes of light also elicited field-evoked potentials. Judging by its behavior, it is very likely that this deformed cat had completely lost its ability to perceive images, but had probably retained some sensitivity to light.     

Frequency-specific effects on cochlear responses during activation of the inferior colliculus in the Guinea pig

The inferior colliculus (IC) is a major processing center in the ascending auditory pathway. The role of the IC in the descending efferent auditory system is less clear. Although the IC central nucleus (ICC) is the major relay station for the ascending auditory pathways, the IC's cortex receives its main input from the neocortex and nonauditory sources. The goal of this study was to determine if the IC subdivisions had different functions in the descending efferent auditory system. IC subdivisions were identified by their tuning curves evoked by tone stimulation, and the effects of localized electrical stimulation on the cochlear whole-nerve action potential (CAP). Sharp tuning curves were obtained from ICC in contrast to broad tuning curves from the lateral, external cortex. Electrical stimulation within the central nucleus had a sharply tuned effect on the CAP. The frequency region affected within the cochlea closely matched the best frequency of local cells within the central nucleus. The effect of electrical stimulation within the lateral, external cortex on the CAP was smaller in comparison to central nucleus stimulation. Similar to the broad tuning of cells within the lateral cortex, electrical stimulation had a broad frequency effect on CAP thresholds.     

Restoration of visual orienting into a cortically blind hemifield by reversible deactivation of posterior parietal cortex or the superior colliculus

A contralateral hemineglect of the visual field can be induced by unilateral cooling deactivation of posterior middle suprasylvian (pMS) sulcal cortex of the posterior parietal region, and this neglect can be reversed by additional cooling deactivation of pMS cortex in the opposite hemisphere. The purpose of the present study was to test whether an enduring hemianopia induced by removal of all contiguous visual cortical areas of one hemisphere could be reversed by local cooling of pMS cortex in the opposite hemisphere. Two cats sustained large unilateral ablations of the contiguous visual areas, and cooling loops were placed in the pMS sulcus, and in contact with adjacent area 7 or posterior ectosylvian (PE) cortex of the opposite hemisphere. In both instances cooling of pMS cortex, but neither area 7 nor PE, restored a virtually normal level of orienting performance to stimuli presented anywhere in the previously hemianopic field. The reversal was highly sensitive to the extent of cooling deactivation. In a third cat, cooling deactivation of the superficial layers of the contralateral superior colliculus also restored orienting performance to a cortical ablation-induced hemianopia. This reversal was graded from center-to-periphery in a temperature-dependent manner. Neither the cortical ablation nor any of the cooling deactivations had any impact on an auditory detection and orienting task. The deactivations were localized and confirmed by reduced uptake of radiolabeled 2-deoxyglucose to be limited to the immediate vicinity of each cooling loop. The results are discussed in terms of excitation and disinhibition of visual circuits.     

Role of cat primary auditory cortex for sound-localization behavior

Small lesions designed to completely destroy the cortical zone of representation of a restricted band of frequency were introduced within the primary auditory cortex (AI) in adult cats. Physiological mapping was used to guide placement of lesions. Sound-localization performance was evaluated prior to and after induction of these lesions in a seven-choice free-sound-field apparatus. All tested cats had profound contralateral hemifield deficits for the localization of brief tones at frequencies roughly corresponding to those whose representations were destroyed by the lesion. Sound-localization performance was normal at all other test frequencies. In a single adult cat, a massive lesion destroyed nearly all auditory cortex unilaterally, with only the representation of a narrow band of frequency within AI spared by the lesion. This cat had normal abilities for azimuthal sound localization across that frequency band but a profound contralateral deficit for the azimuthal localization of brief sounds at all other frequencies. Recorded sound-localization deficits were permanent. Localization of long-duration tones was not affected by a unilateral AI lesion. These studies indicate that, at least in cats, AI is necessary for normal binaural sound-localization behavior; among auditory cortical fields, AI is sufficient for normal binaural sound-localization behavior; sound-location representation is organized by frequency channel in the auditory forebrain; and AI in each hemisphere contributes to only contralateral free-sound-field location representation.     

Modulatory effect of cortical activation on the lemniscal auditory thalamus of the Guinea pig

In the present study, we investigated the point-to-point modulatory effects from the auditory cortex to the thalamus in the guinea pig. Corticofugal modulation on thalamic neurons was studied by electrical activation of the auditory cortex. The modulation effect was sampled along the frontal or sagittal planes of the auditory thalamus, focusing on the ventral division (MGv) of the medial geniculate body (MGB). Electrical activation was targeted at the anterior and dorsocaudal auditory fields, to which the MGv projects and from which it assumptively receives reciprocal projections. Of the 101 MGv neurons examined by activation of the auditory cortex through passing pulse trains of 100-200 microA current into one after another of the three implanted electrodes (101 neurons x 3 stimulation sites = 303 cases), 208 cases showed a facilitatory effect, 85 showed no effect, and only 10 cases (7 neurons) showed an inhibitory effect. Among the cases of facilitation, 63 cases showed a facilitatory effect >100%, and 145 cases showed a facilitatory effect from 20-100%. The corticofugal modulatory effect on the MGv of the guinea pig showed a widespread, strong facilitatory effect and very little inhibitory effect. The MGv neurons showed the greatest facilitations to stimulation by the cortical sites, with the closest correspondence in BF. Six of seven neurons showed an elevation of the rate-frequency functions when the auditory cortex was activated. The comparative results of the corticofugal modulatory effects on the MGv of the guinea pig and the cat, together with anatomical findings, hint that the strong facilitatory effect is generated through the strong corticothalamic direct connection and that the weak inhibitory effect might be mainly generated via the interneurons of the MGv. The temporal firing pattern of neuronal response to auditory stimulus was also modulated by cortical stimulation. The mean first-spike latency increased significantly from 15.7 +/- 5.3 ms with only noise-burst stimulus to 18.3 +/- 4.9 ms (n = 5, P < 0.01, paired t-test), while the auditory cortex was activated with a train of 10 pulses. Taking these results together with those of previous experiments conducted on the cat, we speculate that the relatively weaker inhibitory effect compared with that in the cat could be due to the smaller number of interneurons in the guinea pig MGB. The corticofugal modulation of the firing pattern of the thalamic neurons might enable single neurons to encode more auditory information using not only the firing rate but also the firing pattern.