Seeing or not seeing where your hands are

Previous findings have demonstrated the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. A strong modulatory effect of vision on touch perception was found when a visual stimulus was presented near the hand. In contrast, when the visual stimulus was presented far from the hand, only a weak modulatory effect was found. The aim of the present study was to verify whether such cross-modal links between touch and vision in the peripersonal space centered on the hand could be mediated by proprioceptive signals specifying the current hand positions or if they directly reflect an interaction between two sensory modalities, i.e., vision and touch. To this aim, cross-modal effects were studied in two different experiments: one in which patients could see their hands and one in which vision of their hands was prevented. The results showed strong modulatory effects of vision on touch perception when the visual stimulus was presented near the seen hand and only mild effects when the vision of the hand was prevented. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand, and corresponding visual receptive fields in the space immediately adjacent to the tactile fields. One important feature of these bimodal neurons is that their responsiveness to visual stimuli delivered near the body part is reduced or even extinguished when the view of the body part is prevented. This implies that, at least for the hand, the vision of the hand is crucial for determining the spatial mapping between vision and touch that takes place in the peripersonal space. In contrast, the proprioceptive signals specifying the current hand position in space do not seem to be relevant in determining the cross-modal interaction between vision and touch.     

Control of single-joint movements in deafferented patients: evidence for amplitude coding rather than position control

Two deafferented patients and several control subjects participated in a series of experiments to investigate how accurate single-joint movements are programed, spatially calibrated, and updated in the absence of proprioceptive information. The deafferented patients suffered from a permanent and severe loss of large sensory myelinated fibers below the neck. Subjects performed, with and without vision, sequences of forearm supinations and pronations with two temporal delays between each movement (0 s and 8 s). Overall, the lack of proprioception did not yield any significant decrease in movement accuracy when vision was available. Without vision, the absence of proprioceptive afferents yielded (1) significantly larger spatial errors, (2) amplitude errors similar to those of control subjects, and (3) a significant drift when an 8-s delay was introduced between two successive movements. Subjects also performed, without vision, a 20 supination followed by a 20 pronation that brought back the wrist to the starting position. On some trials, the supination was blocked unexpectedly by way of a magnetic brake. When the supination was blocked, subjects were already on the second target and no pronation was required when the brake was released. The defferented patients, unaware of the procedure, always produced a 20 pronation. These data confirm that deafferented patients were not coding a final position. It rather suggests that they coded an amplitude and translated the spatial distance between the two targets in a corresponding force pulse. Overall, the results highlight the powerful and key role of proprioceptive afferents for calibrating the spatial motor frame of reference.     

Visual responses with and without fixation: neurons in premotor cortex encode spatial locations independently of eye position

 The ventral premotor cortex (PMv) of the macaque monkey contains neurons that respond both to visual and to tactile stimuli. For almost all of these “bimodal” cells, the visual receptive field is anchored to the tactile receptive field on the head or the arms, and remains stationary when the eyes fixate different locations. This study compared the responses of bimodal PMv neurons to a visual stimulus when the monkey was required to fixate a spot of light and when no fixation was required. Even when the monkey was not fixating and the eyes were moving, the visual receptive fields remained in the same location, near the associated tactile receptive field. For many of the neurons, the response to the visual stimulus was significantly larger when the monkey was not performing the fixation task. In control tests, the presence or absence of the fixation spot itself had little or no effect on the response to the visual stimulus. These results show that even when the monkey’s eye position is continuously changing, the neurons in PMv have visual receptive fields that are stable and fixed to the relevant body part. The reduction in response during fixation may reflect a shift of attention from the visual stimulus to the demands of the fixation task. Received: 8 April 1997 / Accepted: 16 July 1997     

The projection from the olfactory epithelium to the olfactory bulb in the salamander, Ambystoma tigrinum

Summary Odor quality may be represented as a topographic code of responses of receptor cells throughout the olfactory epithelium, with this code conveyed to the central nervous system by a topographic projection from the olfactory epithelium to the olfactory bulb. There is good evidence for topographic differences in odor-induced receptor cell activity in the tiger salamander but there is no evidence for a topographic epithelium-to-bulb projection in this species. In the present study ³H-leucine autoradiography was used to trace the projections of olfactory receptor neurons in the tiger salamander. Thirteen animals received small injections of tritiated leucine into different regions of the dorsal or the ventral olfactory epithelium, or into the ventrolateral, vomeronasal organ. The results show that the anterior-to-posterior axes in the dorsal and ventral epithelia are represented along the ventral-to-dorsal axis in the rostral end of the olfactory bulb. The vomeronasal organ projects to the caudal end of the bulb. We conclude that the central projection of the olfactory epithelium in the tiger salamander is topographically organised only along the antero-posterior axis and not the medio-lateral axis. Thus epithelial receptor cell activity along the antero-posterior axis would be represented in the glomerular layer of the bulb by activity along its ventro-dorsal axis.     

Neuronale reaktionen im tectum opticum der katze auf bewegte und stationäre lichtreize

Zusammenfassung Es wurden 80 Einheiten des Tectum opticum der Katze abgeleitet und ihre Reaktionen auf stationäre und bewegte optische Reize geprüft.Neben den Neuronen, die in ihrer Reaktionsweise retinalen Einheiten vergleichbar waren, fanden sich überwiegend (89%) Neurone, die auf bewegte optische Reize reagierten. Unter den letzteren zeigte die Mehrheit (70%) richtungsspezifisches Verhalten. Bei einigen Neuronen war in einem beschränkten Bereich von 1–7.5/sec die Reaktion gesetzmäßig abhängig von der Winkelgeschwindigkeit des Bewegungsreizes (Potenzfunktion mit dem Exponenten 0.67). Die rezeptiven Felder waren meist rund mit einem durchschnittlichen Durchmesser von 8.1 (3–22). 68% der Einheiten reagierten nicht auf diffusen Lichtreiz. Die Reaktionen auf nicht bewegte Punktlichtreize waren rasch adaptierend und inkonstant in ihrer Art und Stärke. In kurzen Abständen mehrfach wiederholte Bewegungsreize bewirkten bei einem Teil der Bewegungsneurone rasche Adaptation.Zwei kurz aufeinander folgende Punktlichtreize ergaben eine Reaktion, die niedriger als die Summe der Erregungen der jeweils einzeln gegebenen Lichtreize war, wenn die zeitliche Folge der beiden Reize der Vorzugsrichtung des Neurons entgegengesetzt war. Bei Reizfolgen entsprechend der Vorzugsrichtung entsprach die Gesamtreaktion der Summe der Einzelreizantworten. Dies läßt vermuten, daß die Richtungsspezifität durch unilaterale Hemmung bedingt ist.

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Summary Recordings were made from 80 single units in cat's Tectum opticum during visual stimulation with moving and stationary optic stimuli. The majority of units (89%) showed movement specific reactions, the rest behaved functionally similar to retinal or geniculate neurons. 70% of the movement specific units showed directional selective reactions. The receptive fields, as determined with stationary and moving stimuli were mostly circular with an average diameter of 8.1° (range 3–22°). Stimuli passing through the periphery of the field led to less pronounced reactions than those going through the center. In 10 out of 30 units, the relation between discharge rate and angular velocity in a restricted range from 1°–7.5°/sec could be approximated by a power function with an exponent of 0.67. Above 10°/sec irregular and unsystematic alterations of reactivity were observed. 68% of the tectal units recorded did not respond to diffuse light stimuli. The reactions to localized intermittent stationary light stimuli were mostly off (42%) or on-off-responses (19%) and were characterized by fast adaptation, change of reaction type during successive intermittent stimulation and by the absence of an antagonistic field-structure. Stimulation of adjacent points in a temporal sequence corresponding to movement opposite to the most sensitive direction of a directional specific neuron led to a reaction which was below the sum of the reaction of the two stimuli given alone. At a temporal sequence of the two stimuli such as to simulate the most sensitive direction, the resulting reaction corresponded to the sum of the reactions of both stimuli given alone. This suggests a mechanism of unilateral inhibition to be responsible for directional selectivity.

Wir danken Priv.-Dozent Dr. O.D. Creutzfeldt für Beratung und Diskussion bei Durchführung der Experimente und Abfassung des Manuskriptes, Herrn Wickelmaier für seine tatkräftige Hilfe bei technischen Problemen der Versuchsanordnung.     

弧菌,气单胞菌及邻单胞菌编码鉴定研究

采用编码技术对医学常见的弧菌属、气单胞菌属及邻单胞菌属的１２ 个菌种进行编码,建立了７ 位数编码鉴定法。并用此法鉴定了２０８ 株标准菌株,与常规鉴定法比较,两法无显著统计学意义（χ２ ＝０－４４ ,Ｐ＞０－０５）,符合率为９５－６７％ 。此鉴定法快捷、可靠、操作简便、判定结果简单、适合于临床、卫生及基层微生物实验室推广应用。     

基于自适应方向滤波的左心室轮廓提取

提出基于自适应方向滤波方法来提取左心室轮廓。在噪声的干扰下,引入经平滑处理的方向滤波能够得到精确的边缘,所获得的边缘方向矢量能够在边缘跟踪时对边缘走向预测,同时对参数进行自适应地调整。通过尽量少的人机交互,算法能够自动提取出左心室的轮廓。实验证明该算法增加了边缘提取的精度和一致性,同时显著地降低了计算复杂度。     

Single neurons are differently involved in stimulus-specific oscillations in cat visual cortex

Synchronised oscillatory population events (35–80 Hz; 60–300 ms) can be induced in the visual cortex of cats by specific visual stimulation. The oscillatory events are most prominent in local slow wave field potentials (LFP) and multiple unit spikes (MUA). We investigated how and when single cortical neurons are involved in such oscillatory population events. Simultaneous recordings of single cell spikes, LFP and MUA were made with up to seven microelectrodes. Three states of single cell participation in oscillations were distinguished in spike triggered averages of LFP or MUA from the same electrode: (1) Rhythmic states were characterised by the presence of rhythmicity in single cell spike patterns (35–80 Hz). These rhythms were correlated with LFP and MUA oscillations. (2) Lock-in states lacked rhythmic components in single cell spike patterns, while spikes were phase-coupled with LFP or MUA oscillations. (3) During non-participation states LFP or MUA oscillations were present, but single cell spike trains were neither rhythmic nor phase coupled to these oscillations. Stimulus manipulations (from optimal to suboptimal for the generation of oscillations) often led to systematic transitions between these states (from rhythmic to lock-in to non-participation). Single cell spike coupling was generally associated with negative peaks in LFP oscillations, irrespective of the cortical separation of single cell and population signals (0–6 mm). Our results suggest that oscillatory cortical population activities are not only supported by local and distant neurons with rhythmic spike patterns, but also by those with irregular patterns in which some spikes occur phase-locked to oscillatory events.     

The mechanism of directional coronary atherectomy

An attempt was made to assess the mechanism of directional coronaryatherectomy using different methods of analysis. Quantitativecoronary angiography was used as the gold standard to assessthe immediate results of atherectomy, and a comparative quantitativeanalysis of atherectomy and balloon angioplasty was made. Todetermine whether the post-atherectomy cross-sectional areais close to a circle, we compared the area measurements obtainedby edge detection with those obtained by videodensitometry.Finally, the extent of a ‘Dotter’ effect was establishedby quantitative angiography following crossing the stenosiswith the atherectomy device. For the purpose of this study,the results of the first 113 successful atherectomy procedureswere reviewed. In matched lesions, directional atherectomy induceda greater increase in minimal luminal diameter than balloonangioplasty (1.6 mm vs 0.8 mm; P < 0.0001 However, this luminalimprovement is due to a substantial ‘Dotter’ effectinduced by the bulky atherectomy device. Following atherectomy,only a slight difference in cross-sectional area measurementsbetween edge detection and videodensitometry (mean difference:0.28 mm² was found. Histologic examination of an atherectomizedcoronary artery showed a near-circular post atherectomy areageometry. In conclusion, directional atherectomy is a very effectivedevice with a substantially better initial result than balloonangioplasty. However, insertion of this bulky device itselfcauses an important ‘Dotter’effect.     

Ⅰ型疫苗衍生脊髓灰质炎病毒循环的发现和基因特点

目的分析贵州省2004年Ⅰ型循环的疫苗衍生脊髓灰质炎(脊灰)病毒(cVDPVs)的基因特征,阐述cVDPVs的出现为全球消灭脊灰带来的挑战。方法2004年中国疾病预防控制中心(CDC)病毒病预防控制所国家脊灰实验室对各个省送检的每1个脊灰病毒分离株进行聚合酶链反应-限制性酶切片段长度多态性分析(PCR-RFLP)和酶联免疫吸附试验(ELISA)两种方法的型内鉴定。毒株型内鉴别显示异常时,则对该株病毒进行VP1编码区全基因的序列测定和分析。结果2004年从贵州省CDC送检的脊灰病毒株(或粪便标本的复核)中,共发现9株Ⅰ型疫苗衍生脊灰病毒(VDPVs)。这9株VDPVs从2例急性弛缓性麻痹(AFP)病例和4名接触者的粪便标本中分离到。其中8株分离于贞丰县挽兰乡的2例AFP病例和3名接触者,另外1株分离于贞丰县白层镇的1名AFP病例接触者。结论对9株cVDPVs的VP1编码区的序列测定和分析证实,它们有相似的核苷酸序列,共享5个核苷酸突变位点,说明VDPVs已发生了循环。cVDPVs很可能来源于2003年秋季的1次口服脊灰减毒活疫苗病毒的传播。对其中5株VDPVs的3D区和1株VDPV(8229-2)的全序列测定和分析,未发现脊灰病毒血清型之间的重组,也未发现与非脊灰肠道病毒的重组。