胫骨近端后侧数字化三维形态学测量及临床意义

目的　研究胫骨近端后侧数字化形态学测量的方法,探讨其对胫骨后侧平台骨折诊疗的意义。  方法　对60例健康成人胫骨干燥标本进行CT扫描,图像导入Mimics 10.01软件建立数字化三维模型,测量相关解剖参数,分析其分布规律与相关关系。  结果　后侧正中高度（8.46±1.62）mm,后内侧高度（12.27±1.93）mm,后内侧斜坡长度（14.71±2.27）mm,后内侧平台斜坡角（132.02±11.62）°,后内侧斜坡骨干角（147.28±10.72）°,后外侧高度（11.31±1.74）mm,后外侧斜坡长度（14.45±2.26）mm,后外侧平台斜坡角（124.01±9.81）°,后外侧斜坡骨干角（141.88±9.09）°,所有测量参数双侧差异无统计学意义（P＞0.05）。后正中高度、后外侧高度和后外侧斜坡长度与胫骨全长具有相关性（P＜0.01）。   结论　本研究建立的胫骨近端数字化三维模型仿真度高,解剖参数测量结果精确度高,能为胫骨后侧平台骨折临床治疗和内固定物设计提供解剖学依据。     

Digital fluoroscopic assessment of the scapulohumeral rhythm

Previous studies have shown that abnormal rotation of the scapula is associated with shoulder pathology. Among the methods which have been proposed, planar x-ray measurements are probably the only methods, which enable clinicians to assess accurately and objectively the scapulohumeral function in vivo. The aim of this study was to develop a method for the assessment of scapulohumeral kinematics using digital fluoroscopy. Anteroposterior images of the right glenohumeral joint were taken, in thirty-four healthy males, with the arm at rest, 30°, 60°, 90°, 120°, 150° and maximum abduction, in the scapular plane. High inter- and intra-examiner reliability was observed regarding the arm and scapular angle measurements (ICC = 0.92–0.99). The positioning of the arm at the proposed angles was also highly accurate (< 2.3° misplacement) and reproducible (CV% < 5.3%). The mean radiation dose was 0.075 mSv (± 0.027 mSv). At the resting position the scapula was in slight downward rotation (−2.4° ± 4.3°) and the arm in slight abduction (1.5° ± 6.6°). The mean maximum scapular rotation and the mean maximum arm abduction was 61.4° (± 5.2°) and 162.4°(± 6.6°) respectively. A curvilinear relationship was found between the arm angle (AA) and the scapular angle (SA) (p < 0.0001). The AASA ratio for the entire range of abduction was 2.51. The greatest contribution of the scapula (1.71) achieved at 30°-60° of arm. The high accuracy and reliability of our method and the low radiation recordings suggests that digital fluoroscopy may be considered for further investigation of the scapulohumeral kinematics in both healthy and pathological shoulders.     

Flexibility of the shoulder joint measured as range of abduction in a large representative sample of men and women over 65 years of age

Summary In a representative survey of 1000 elderly men and women aged over 65 years living in their own homes, assessments have been made of flexibility measured as range of shoulder abduction in addition to health status, psychological well-being and reported customary activity. The results for shoulder abduction were approximately normally distributed and the mean values (±1 standard deviation) were as follows: — in men aged 65–74 years, 129 (±14)° and aged over 74 years, 121 (±19)°; in women aged 65–74 years, 124 (±19)° and aged over 74 years, 114 (±22)°. These mean values are about 30° less than those accepted for younger subjects. Nearly half the distribution falls below the accepted threshold level of 120° for adequate function. There were significant effects of sex and age (P<0.001); women had poorer flexibility and the reduction with age amounted to 10° per decade. Multiple regression analysis showed that the effect of age was accounted for in part by health, strength and customary use. The effects of use were most marked in those with some disability. This suggests that maintained or increased use could offset some of the age-related loss of the range of shoulder movement.     

Cortical interactive network during mental rotation of Chinese character

Mental rotation (MR) of Chinese characters has been proposed to employ distinct strategies depending on task difficulty. Cognitive process in MR is associated with multi-component neural networks, and elucidation of specific cortical interactions taking place during MR will assist understanding of the cognitive processes involved. In this study, we investigated cortical interactive networks involved in Chinese character MR tasks of different difficulties. Scalp electroencephalogram (EEG) signals were recorded from nine subjects (male/female = 6/3) during MR of a Chinese character presented at different orientations (0°, ±60°, ±120° and 180°). Partial directed coherence (PDC) analysis based on multivariate Granger causality (GC) was used to assess cortical interactions. At ±60° and ±120°, lateral interactions from right to left counterparts were found in both the parietal and motor-related areas, and they were enhanced with the increase of rotation angle. The main interactions between parietal and motor-related areas showed feedforward at rotations of ±60° and ±120°, while feedback interactions appeared at rotations of ±120°. However, at 180° of rotation, neither lateral interactions within motor-related areas nor feedback interactions from motor-related to parietal areas were found. These findings show that during MR of Chinese character (1) cortical interactive networks change according to task difficulty, and (2) the right hemisphere plays an initiating role in bilateral cortical activation.     

Modulation of vergence by off-vertical yaw axis rotation in the monkey normal characteristics and effects of space flight

Horizontal movements of both eyes were recorded simultaneously using scleral search coils in 2 rhesus monkeys before and after the COSMOS 2229 spaceflight of 1992–1993. Another 9 monkeys were tested at comparable time intervals and served as controls. Ocular vergence, defined as the difference in horizontal position between the left and right eyes, was measured during off-vertical yaw axis rotation (OVAR) in darkness. Vergence was modulated sinusoidally as a function of head position with regard to gravity during OVAR. The amplitude of peak-to-peak modulation increased with increments in tilt of the angle of the rotational axis (OVAR tilt angle) that ranged from 15° to 90°. Of the 11 monkeys tested, 1 had no measurable modulation in vergence. In the other 10, the mean amplitude of the peak to peak modulation was 5.5°±1.3° at 90° tilt. Each of these monkeys had maximal vergence when its nose was pointed close to upward (gravity back; mean phase: -0.9°±26°). After space flight, the modulation in vergence was reduced by over 50% for the two flight monkeys, but the phase of vergence modulation was not altered. The reduction in vergence modulation was sustained for the 11-day postflight testing period. We conclude that changes in vergence are induced in monkeys by the sinusoidal component of gravity acting along the naso-occipital axis during yaw axis OVAR, and that the modulation of the vergence reflex is significantly less sensitive to linear acceleration after space flight.     

无症状青年人群股骨颈α角CT测量多个平面之间的比较

目的　比较无症状青年人群中多个平面CT测量股骨颈α角的差异，并对凸轮型股髋撞击综合征（FAI）形态改变的发生率进行评估。  方法　回顾性分析2009年5月至2013年11月120例无髋关节病症患者（20～40岁）的腹部或盆腔CT扫描资料。α角的测量采用平行于股骨颈长轴的斜轴位平面以及以股骨颈中心作为旋转轴的4个方向辐射状层面,两者差异的比较采用方差分析，α角大于55°提示凸轮型FAI形态异常。  结果　斜轴位平面α角均值为(39.5±6.51) º，共有12人（占10%，12/120）、14个关节α角大于55 º，10人为单侧、2人为双侧；在12点、1点、2点及3点方向各平面的α角均值分别为(42.8±7.3) º,(48.8±7.6)º,(47.3±7.2)º,(40.2±6.7)º，在所有辐射状平面中共有106个关节α角大于55 º，其中在1:00方向有54个关节α角增大，占受试者的35%（42 /120）（30人为单侧，12人为双侧）；斜轴位平面与12点、1点、2点方向平面测量的α角之间的差异有统计学意义（P<0.05）。  结论　在辐射状平面测量α角可能更准确；无症状青年人群中，其类似凸轮型FAI的形态改变有较高的发生率。     

Specificity of joint angle in isometric training

Summary Six healthy women (21.8±0.4 y) did isometric strength training of the left plantarflexors at an ankle joint angle of 90°. Training sessions, done 3 times per week for 6 weeks, consisted of 2 sets of ten 5 s maximal voluntary contractions. Prior to and following the training, and in random order, voluntary and evoked isometric contraction strength was measured at the training angle and at additional angles: 5°, 10°, 15°, and 20° intervals in the plantarflexion and dorsiflexion directions. Evoked contraction strength was measured as the peak torque of maximal twitch contractions of triceps surae. Training increased voluntary strength at the training angle and the two adjacent angles only (p<0.05). Time to peak twitch torque was not affected by training. Twitch half relaxation time increased after training (p=0.013), but the increase was not specific to the training angle. There was a small (1.1%, p<0.05) increase in calf circumference after training. Evoked twitch torque did not increase significantly at any joint angle. It was therefore concluded that a neural mechanism is responsible for the specificity of joint angle observed in isometric training.     

Anatomical evaluation and clinical importance of the tibiofibular syndesmosis ligaments

The aim of this study was to describe the detailed anatomical arrangement of ligaments of the tibiofibular syndesmosis and to highlight the clinical aspects of fracture dislocations. This study was performed on 42 legs of adult human embalmed cadavers. Tibiofibular syndesmosis ligaments attachments and their mutual relationships were described and their dimensions were measured. The anterior tibiofibular ligament is usually composed of three parts. This ligament runs obliquely at laterodistaly direction making 35° angle with horizontal plane and posteriorly 65° angle with sagittal plane. The posterior tibiofibular ligament runs almost horizontally 20° angle with horizontal plane. The mean thicknesses of tibial and fibular attachments are 6.38±1.91 mm and 9.67±1.74 mm, respectively. The inferior transverse ligament originates from just below the posterior tibiofibular ligament, which has variations on the shape and dimensions due to its attachment points. The average length is 36.60±9.51 mm. The network between the fibular notch and the distal fibula has been filled with the interosseous tibiofibular ligament whose fibers follow the laterodistal and anterior direction from the tibia to the fibula. It lies proximally 30–40 mm from the mortise. At the inferior view of the tibiofibular syndesmosis a pyramidal shaped cartilaginous facet was observed which was attached to the fibula. The length of this cartilage was variable. Some of synovial plicas from the ankle joints synovial membrane were observed at this view. We conclude that the results of this study may be useful to both orthopedic surgeons and radiologists for anatomic evaluation of the tibiofibular syndesmosis area.     

关节镜下膝内侧支持带紧缩外侧支持带松解治疗髌骨脱位

目的 　探讨关节镜下膝内侧支持带紧缩外侧支持带松解术在治疗髌骨脱位中的临床疗效。 方法 自2009 年3 月～2011年7月收治25 例25膝髌骨脱位,术前未接受过外科手术治疗。术中关节镜监视下松解外侧支持带并紧缩缝合内侧支持带。术后行正规康复训练。随访18～24个月,了解膝关节脱位复发情况及患膝功能恢复情况。 结果　术后无髌骨脱位复发,手术前后Lysholm 膝关节功能综合评分分别为（59.00±13.37）分和 （92.14±5.15）分（P＜0.05）;手术后影像测量对比髌骨适合角从术前（21.10±5.61）°纠正到（-1.70±7.41）°(P＜0.05);外侧髌股角从术前（-1.3±1.6）°纠正到（6.1±1.4）°(P＜0.05）,上述3项指标手术前后比较,均有统计学差异。 结论　关节镜辅助下膝内侧支持带紧缩配合外侧支持带松解术治疗髌骨脱位,手术创伤小,疗效满意。     

Static roll and the vestibulo-ocular reflex (VOR)

Summary We measured the effect of static lateral tilt (roll) on the gain and time constant of the vestibulo-ocular reflex (VOR) in five normal subjects by recording both the horizontal and vertical components of eye velocity in space for rotation about an earth vertical axis with the head either upright or rolled to either side. The time constant of the VOR in the upright position was 19.6 ±3.2s (mean ± standard deviation). The time constant of the horizontal component with respect to the head decreased to 15.7±4.0s for 30° roll and to 12.7±2.7s for 60° roll. The time constant of the vertical component with respect to the head was 11.0±1.4 s for 30° roll and 7.5±1.6 s for 60° roll. The gain of the horizontal VOR with respect to space did not vary significantly with roll angle but a small space-vertical component to the VOR appeared during all rotations when the head was rolled away from upright. This non-compensatory nystagmus built up to a maximum of 2–3°/s at 17.0±4.7s after the onset of rotation and then decayed. These data suggest that static otolith input modulates the central storage of semicircular canal signals, and that head-horizontal and head-vertical components of the VOR can decay at different rates.     

Origin and initial course of the renal arteries a radiological study

The aim of this study was to determine the topography of the origin, implantation angle and initial course of the renal arteries in the transverse and frontal planes, from a prospective analysis of angiograms and helical CT-scans of 40 patients. In the frontal plane, the implantation angles of the right and left renal arteries were 73.8 ± 17° axsnd 65.6 ± 16° respectively 17.9% of the right renal arteries were straight compared with only 5% of the left ones. The first sinuosity was observed to be at a distance greater than the aortic diameter for 43.6% of right renal arteries and at a distance less than the aortic diameter for 62.5% for the left renal a. In the transverse plane, the right renal a. had an implantation angle of 65.6 ± 15.7° compared with 95.7 ± 16.85% for the left renal a. The artery was rectilinear in 2.6% of the cases on the right side, and in 2.5% of the cases on the left. The first sinuosity occurred before the lateral margin of the spine was reached in 60.5% of right renal arteries and after the margin of psoas major muscle for 55% of left renal arteries. A knowledge of the anatomy of the origin and initial course of the renal arteries is important when considering vessel dilatation and the implantation of stents in the renal arteries. No correlation was observed between the origin, sinuosity or angulation of the renal arteries which could aid interventional procedures.     

Temperature dependence of soleus H-reflex and M wave in young and older women

The purpose of this study was to investigate the effect of altered local temperature on soleus H-reflex and compound muscle action potential (M wave) in young and older women. H-reflex and M wave responses were elicited in 10 young (22.3±3.3 years) and 10 older (72.5±3.2 years) women at three muscle temperatures: control (34.2±0.3°C), cold (31.3±0.5°C) and warm (37.1±0.2°C). H-reflex output, expressed as the ratio between maximal H-reflex and maximal M wave (H_max/M_max), was lower in the older, compared with the younger, group, regardless of temperature. In control temperature conditions, for example, the H_max/M_max ratio was 36.8±24% in the young and 25.4±20% in the older (P<0.05). Warming had no effect on the H-reflex output in either group, whilst cooling increased H-reflex output only in the younger group (+28%). In both groups, cooling increased (+5.3%), and warming decreased (–5.5%) the H-reflex latency. This study confirms that older individuals experience a reduced ability to modulate the reflex output in response to a perturbation. In a cold environment, for example, the lack of facilitation in the reflex output, along with a delayed reflex response could be critical to an older individual in responding to postural perturbations thus potentially compromising both static and dynamic balance.     

半椎体所致中重度脊柱侧凸的解剖特点分析及手术选择

目的　通过影像学方法分析单个半椎体所致的中重度脊柱侧凸的解剖特点,根据解剖特点设计手术方案并评价初期手术效果。  方法　中重度先天性脊柱侧凸患者16例,术前行X线、CT检查,分析半椎体位置、生长潜质、类型以及脊柱的侧后凸Cobb角、柔韧度,根据解剖特点选择后路截骨矫形、后路截骨矫形加前路植骨支撑术,评价术后临床疗效。  结果　患者均顺利完成手术,手术时间4.0～8.0 h,平均5.8 h ;术中出血量500～4000 mL,平均1350 mL。术前侧凸（67.8±8.4）°,术后（25.3±6.8）°,矫正率(63.1±6.1) %。术前后凸Cobb角为（73.5±10.7）°,术后（29.1±5.6）°,矫正率(60.1±6.2)%。无脊髓神经损伤、深部感染、深静脉血栓形成等并发症发生。随访X线片证实植骨均融合,未发现内固定物松动断裂、假关节形成等并发症,获得的矫形均无丢失。  结论　脊柱解剖特点对手术操作有指导意义,采用经后路矫正术对中重度先天性脊柱侧凸是一有效、可行的方法,如果半椎体相邻椎体楔形变严重,前路植骨支撑融合术是必要的。     

Static and dynamic changes in body orientation modulate spinal reflex excitability in humans

In the present study, we investigated the modulation pattern of the soleus H reflex in healthy subjects in response to imposed static and dynamic changes in body angle, referenced to the vertical plane. Soleus H reflexes were recorded using conventional methods with subjects either supine or while they were erect. Changes in body angle were initiated with subjects lying supine on a tilt table. Table position was controlled via a motor and could move from the horizontal to the upright position and beyond. Elastic bands around the trunk (upper and lower part) and around the thigh and shank secured subjects' position. In the vertical position, the soleus H reflex exhibited a strong depression in all subjects tested, reaching amplitudes as low as 40±8.1% of the control reflex (Ho). With subjects supine, positioning the body at 10°, 20°, 40°, 60°, 90°, –50° and –20° all resulted in a significant facilitation of the soleus H reflex. The reflex magnitude at these angles ranged from 140±17.2% to 180±10.9% of the Ho. Reflex facilitation was also observed following dynamic tilt of the body in the sagittal plane (at 1.8°/s) with the H reflex reaching amplitudes as high as 300±18.3% of Ho. Our findings indicate that changes in body orientation induced a significant facilitation of the H reflex magnitude in soleus motoneurones that were essentially independent of angular change in body orientation or of movement direction. In addition, they highlight the potent modulatory effects that natural stimulation of the vestibular system can have on reflex excitability. The implications of our findings are discussed in relation to the maintenance of body posture.     

Relative frequency and visual resolution of X- and Y-cells in the LGN of normal and monocularly deprived cats: Interlaminar differences

Summary The visual acuity (spatial resolving power) and the relative incidence of X- and Y-cells in laminae A and A₁ of the dorsal lateral geniculate nucleus (LGN) with receptive fields within 10 ° visual angle to the area centralis have been determined in normal and monocularly deprived cats, using a square-wave grating with logarithmically varying spatial frequencies (0.05–8 c/deg).In the normal cat's LGN the incidence of Y-cells is 1.6 times higher in A₁ (48% of the relay-cells) than in A (29%). The mean spatial resolution of all cells is 1.3 times higher in A (2.5 ± 1.2 c/deg) than in A₁ (1.8 ± 1.0 c/deg). Mean acuity of Y-cells is equal in both laminae (1.1 ± 0.5 c/deg), but for X-cells it is higher in lamina A (2.9 ± 1.0 c/deg in A, vs. 2.5 ± 0.7 c/deg in A₁).After early monocular deprivation, visual acuity is reduced in the deprived lamina A₁ (X-cells: 1.7 ± 0.9 c/deg in A₁ vs. 2.6 ± 0.7 c/deg in A; Y-cells: 0.9 ± 0.4 c/deg in A₁ vs. 1.3 ± 0.4 c/deg in A). This confirms the results of Maffei and Fiorentini (1976). However, visual acuity of X-cells is still higher in the deprived lamina A (3.1 ± 1.0 c/deg) than in the non-deprived lamina A₁ (2.7 ± 0.7 c/deg). For Y-cells, visual acuity is equal in both laminae (1.3 ± 0.5 c/deg). Thus the loss of visual acuity is only significant in lamina A₁. This loss was equally strong in the area centralis and up to 10 ° eccentricity.Ipsilateral to the early deprived eye only 37% of all recorded Y-cells were located in the deprived lamina A₁ (this is 1.7 times less than in the normal A₁). Contralateral to the deprived eye 29% of the Y-cells were recorded in the deprived lamina A (1.3 times less than in the normal A).In conclusion, both the impairment of mean visual acuity and the reduction in the recording probability of Y-cells were more pronounced in lamina A₁ (receiving uncrossed inputs from the deprived eye) than in lamina A (crossed inputs).This study was supported by DFG grant Ho 450/4 to K.-P. Hoffmann and a grant from European Training Programme in Brain and Behaviour Research to R. Sireteanu     

Behaviour of the human gastrocnemius muscle architecture during submaximal isometric fatigue

The purpose of this study was to examine whether the human gastrocnemius medialis (GM) fascicle length and pennation angle alter during a sustained submaximal isometric plantar flexion. Fourteen male subjects performed maximal voluntary plantar flexions (MVC) on a dynamometer before and after a fatiguing task. This task consisted of a sustained submaximal isometric fatiguing contraction (40% MVC) until failure to hold the defined moment. Ultrasonography was used to visualise the muscle belly of the GM. Leg kinematics were recorded (120 Hz) to calculate the joint moment using inverse dynamics. The exerted moments and the EMG signals from GM and lateralis, soleus and tibialis anterior were measured at 1,080 Hz. The root mean square (RMS) of the EMG signal of the three triceps surae muscles increased significantly (P0.05) between 17% and 28% with fatigue. Further, the fascicle length of the GM significantly decreased from 47.1±8.0 mm at the beginning to 41.8±6.7 mm at the end of fatigue and the pennation angle increased from 23.5±4.1° to 26.3±2.2° (P0.05). The changes in fascicle length and pennation angle of the GM during the contraction can influence the force potential of the muscle due to the force–length relationship and the force transmission to the tendon. This provides evidence on that an additional mechanical mechanism, namely tendon creep, can contribute to the increase in the EMG activity of the GM during submaximal isometric sustained contractions.     

Strain and elongation of the vastus lateralis aponeurosis and tendon in vivo during maximal isometric contraction

The strain and elongation of the vastus lateralis (VL) tendon, tendon plus aponeurosis, and aponeurosis were examined during maximal voluntary contractions on a Biodex-dynamometer (knee angle 115°, hip angle 140°) in 12 sprinters. Following a warm-up phase, the subjects were instructed to perform a gradual maximal knee extension and hold it for about 3 s. The kinematics of the leg were recorded using a Vicon 512 system with eight cameras operating at 120 Hz. Ultrasonography images were taken simultaneously from the VL myotendinous junction and the mid lateral part of the VL muscle belly. During the maximal isometric knee extensions, the knee joint rotated (13.6±5.9°), leading to an overestimation of the elongation of the tendinous tissues. After correcting for this, the maximal elongation of the VL tendon examined at the myotendinous junction was lower (P<0.05) than the maximal elongation of the VL tendon plus aponeurosis examined at the muscle belly (15 vs. 27 mm, respectively). The maximal estimated strains of the tendon, tendon plus aponeurosis, and aponeurosis showed no statistical differences (8±2%, 8±1%, and 7±2%, respectively, P>0.05). It is concluded that the strains of the human VL tendon, VL tendon plus aponeurosis, and VL aponeurosis, as estimated in vivo by two dimensional ultrasound during maximal isometric contractions, do not differ from each other. The displacement measured at a cross point in the VL muscle belly is significantly greater than that measured at the VL myotendinous junction.     

Estimation of Cardiac Conduction Velocities Using Small Data Sets

Cardiac surface conduction velocities could provide valuable information about the speed and angle of a propagating electrical wave front. It would be advantageous to develop catheter-based velocity mapping devices to improve the visualization of cardiac arrhythmias. However, catheter tip size is limited to 2.5 mm in diameter, restricting the number and size of electrodes that can be placed on a catheter tip. We address the feasibility of estimating conduction speed and angle from small data sets suitable for recording from a catheter device in a standard clinical environment. We estimated cardiac conduction velocities from data subsets of 4–7 closely spaced electrograms, and then compared these estimates to velocities estimated from a larger reference grid. We studied 137 ventricular beats and 17,756 velocity vectors from six swine hearts. Average differences in angle between the two estimates were 0.4° ± 16° while average differences in speed were 5% ± 33%. These angle and speed differences provide an initial quantitative assessment of velocity accuracy for the purposes of catheter-based vector mapping. © 2003 Biomedical Engineering Society. PAC2003: 8719Hh, 8719Nn, 8780-y     

Mechanical properties of dilated human ascending aorta

Dilation of the ascending aorta, associated with Marfan Syndrome, bicuspid aortic valve, or advanced age, may lead to aortic dissection and rupture. Mathematical models can be used to assess the relative importance of increased wall stresses and decreased strength in these mechanical failures. To obtain needed inputs for such models, mechanical properties of dilated human ascending aorta were measured in vitro. Specimens for opening angle, biaxial elastic, and uniaxial circumferential strength tests were cut from excised tissue obtained from 54 patients (age 18–81 years) undergoing elective aortic graft replacement surgery. Opening angle was significantly greater in patients older than 50 years (262°±76°, n=21) compared to younger patients (202°±70°, n=13 All biaxial elastic specimens n=40 exhibited nonlinear stress-strain behavior. Rapid increases in circumferential and axial stresses occurred at lower strains in the older patient group than in the younger. Mean strength was significantly lower in older patients (1.35±0.37 MPa, n=14) than younger (2.04 ± 0.46 MPa, n=11, age <50 years). These changes in mechanical properties suggest that age may influence the risk of aortic dissection or rupture of dilated ascending aorta. © 2002 Biomedical Engineering Society. PAC2002: 8719Rr, 8719Hh     

Inactivation of the infragranular striate cortex broadens orientation tuning of supragranular visual neurons in the cat

Intracortical inhibition is believed to enhance the orientation tuning of striate cortical neurons, but the origin of this inhibition is unclear. To examine the possible influence of ascending inhibitory projections from the infragranular layers of striate cortex on the orientation selectivity of neurons in the supragranular layers, we measured the spatiotemporal response properties of 32 supragranular neurons in the cat before, during, and after neural activity in the infragranular layers beneath the recorded cells was inactivated by iontophoretic administration of GABA. During GABA iontophoresis, the orientation tuning bandwidth of 15 (46.9%) supragranular neurons broadened as a result of increases in response amplitude to stimuli oriented about ±20° away from the preferred stimulus angle. The mean (±SD) baseline orientation tuning bandwidth (half width at half height) of these neurons was 13.08±2.3°. Their mean tuning bandwidth during inactivation of the infragranular layers increased to 19.59±2.54°, an increase of 49.7%. The mean percentage increase in orientation tuning bandwidth of the individual neurons was 47.4%. Four neurons exhibited symmetrical changes in their orientation tuning functions, while 11 neurons displayed asymmetrical changes. The change in form of the orientation tuning functions appeared to depend on the relative vertical alignment of the recorded neuron and the infragranular region of inactivation. Neurons located in close vertical register with the inactivated infragranular tissue exhibited symmetric changes in their orientation tuning functions. The neurons exhibiting asymmetric changes in their orientation tuning functions were located just outside the vertical register. Eight of these 11 neurons also demonstrated a mean shift of 6.67±5.77° in their preferred stimulus orientation. The magnitude of change in the orientation tuning functions increased as the delivery of GABA was prolonged. Responses returned to normal approximately 30 min after the delivery of GABA was discontinued. We conclude that inhibitory projections from neurons within the infragranular layers of striate cortex in cats can enhance the orientation selectivity of supragranular striate cortical neurons.