Impairment and recovery of visual functions after bilateral lesions of superior colliculus

Adult, male hooded rats were tested on a six-choice jumping stand apparatus designed to study their ability to perform visually guided orientation movements with a brightness discrimination task. Upon reaching criterion, the rats suffered either one- or two-stage, bilateral electrolytic lesions of the superior colliculi and then, after a brief recovery period, were retested for their ability to retain the preoperatively learned task and, in addition, perform a more difficult task. Although both brain damaged groups evidenced an impairment in comparison to sham-operated controls, the rats with two-stage lesions were less disabled than their simultaneously operated counterparts.     

Studies on cortical field potentials recorded during learning processes of visually initiated hand movements in monkeys

Summary A monkey was trained to lift a lever by wrist extension in response to a light stimulus. During the learning process of the task over several months, field potentials related not only to the task performance but also to substitution and stimulation experiments were recorded with chronically implanted electrodes on the surface and at a depth of 2.5–3.0 mm in the prefrontal, premotor, motor and prestriate cortices. In the substitution experiment, an examiner lifted a lever for the monkey so that it was watching the light and rewarded without the hand movement. In the stimulation experiment, the same light stimulus was simply delivered to the monkey. In a naive monkey which lifted the lever independently of the stimulus, stimulus-locked potentials were evoked by the task experiment in those cortices except the motor cortex, but none was elicited by the substitution or stimulation experiment. In a welltrained monkey, the substitution and stimulation experiments induced almost the same potentials as those prior to the task movement in respective cortices except the motor cortex, in which the component of cerebellar-induced premovement potential was not observed during the substitution and stimulation experiments. At an intermediate stage of learning, the situation was intermediate between the naive and well-trained stages and most premovement potentials except those in the motor cortex were elicited by the substitution experiment in reduced sizes, but nothing by the stimulation experiment.The present study suggests that the neuronal circuits for the operantly conditioned movement are functionally organized and gradually consolidated in the learning process, and that the consolidation is made earlier for the circuit involving association and premotor cortices than the circuit including the motor cortex in the process. The circuit to the motor cortex via the cerebro-cerebellar interconnection is recruited only on the execution of movement.     

Interference between velocity-dependent and position-dependent force-fields indicates that tasks depending on different kinematic parameters compete for motor working memory

Humans demonstrate motor learning when exposed to changes in the dynamics of movement or changes in the visuomotor map. However, when two opposing dynamic transformations are learned in succession, the memory of the first is overwritten by learning of the second; the same is true for two opposing visuomotor rotations. This retrograde interference is not seen for all combinations of transformations, however. When a dynamic transformation is learned subsequent to a visuomotor rotation, the presence or absence of interference appears to depend crucially on the structure of the dynamic task: a force-field dependent on the position of the hand produces interference, whereas an inertial load applied lateral to the hand does not. To explain these results, it has been hypothesized that two transformations can be learned without interference if they depend on two different kinematic parameters of movement (such as position and velocity of the hand). Here we demonstrate, contrary to this hypothesis, interference between a dynamic transformation that depends on the position of the hand and one that depends on its velocity. However, the interference was found to be incomplete, supporting the view that the ability to retain motor memories for different tasks depends on the degree to which their representations conflict in working memory.     

A neural network-based similarity index for clustering DNA microarray data

A common approach to the analysis of gene expression data is to define clusters of genes that have similar expression. A critical step in cluster analysis is the determination of similarity between the expression levels of two genes. We introduce a neural network-based similarity index as a non-linear similarity index and compare the results with other proximity measures for Saccharomyces cerevisiae gene expression data. We show that the clusters obtained using Euclidean distance, correlation coefficients, and mutual information were not significantly different. The clusters formed with the neural network-based index were more in agreement with those defined by functional categories and common regulatory motifs.     

Operant conditioning studies of taste discrimination in the pigeon (Columba livia)

In the conditioning procedure employed in this study, pigeons were trained to dip their bills into a container and then to peck either at a left or at a right key, depending on whether the container was full of distilled water or of a solution of the substance being tested. The discrimination thresholds found (from one bird each) were 2 g/l (0.034 M) for NaCl, 2 g/l (0.024 M) for NaHCO₃, 1 g/l (0.013 M) for KCl, 0.5 g/l (0.005 M) for KHCO₃. Following the same procedure, two birds were then faced with the choice between the solution of the known substance and of a novel one. A higher degree of discrimination was found between NaHCO₃ and KHCO₃ than between NaHCO₃ and NaCl; in the latter case, choices appeared to be mostly based on the concentration of the two substances.     

非言语型学习障碍儿童社会信息加工的特点

目的: 探讨非言语型学习障碍儿童社会信息加工特点.方法: 本研究为病例对照研究.根据确定学习障碍儿童的标准,先确定学习障碍儿童,然后对学习障碍儿童进行韦氏儿童智力测验,根据测验结果把学习障碍儿童进一步分为非言语型学习障碍组(23人)、言语型学习障碍组(28人),然后按1:1比例选取对照组(51人).设置儿童与同伴、成人相互作用的三类情景,每类情景又分为模糊和清晰两种情况,对三组儿童进行结构性访谈.结果: ①清晰权威情景下.非言语型学习障碍儿童的编码数显著低于对照组儿童[(2.35±1.15)vs.(3.25±1.27),P＜0.01];对人物意图的判断,非言语型学习障碍儿童选择"恶意"的比率(65%)高于言语型学习障碍儿童(29%)(P＜0.05);在工具效能感上,非言语型学习障碍儿童选择有效的比率(74%)高于言语型学习障碍儿童(36%)(P＜0.05).②非言语型学习障儿童在每个情景故事下的总反应数都显著低于对照组儿童[模糊同伴加入情景:(1.17±0.49)vs.(1.09±0.86).P＜0.01;清晰同伴加入情景:(1.09±0.28)vs.(1.69±0.96),P＜0.01;模糊同伴激惹情景:(1.09±0.41)V8.(1.49±0.78),P＜0.05;清晰同伴激惹情景:(1.17±0.49)vs.(1.65±0.95),P＜0.05:模糊权威情景:(0.96±0.36)vs.(1.37±0.72),P＜0.01;清晰权威情景:(1.00±0.30)vs.(1.37±0.59),P＜0.01].结论: ①清晰权威情景下,非言语型学习障碍儿童编码精确性不如对照组儿童;对他人意图的判断非言语型学习障碍儿童比言语型学习障碍儿童倾向于敌意归因;非言语型学习障碍儿童比言语型学习障碍儿童工具效能感高.②在每个情景下,非言语型学习障碍儿童比对照组儿童生成策略少,反应不灵活.     

Scaling of smooth anticipatory eye velocity in response to sequences of discrete target movements in humans

We investigated the ability to generate anticipatory smooth pursuit to sequences of constant velocity (ramp) stimuli of increasing complexity. Previously, it was shown that repeated presentation of sequences composed of four ramps with two speeds in two directions, evoked anticipatory smooth pursuit after only one or two presentations. Here, sequences of four or six ramps, each having a choice of four speeds and either one or two directions (uni- or bi-directional) were examined. The components of each sequence were presented as discrete ramps (duration: 400 ms; randomised velocity: 10–40°/s), each starting from the centre with 1,200 ms periods of central fixation between ramps, allowing anticipatory activity to be segregated from prior eye movement. Auditory warning cues occurred 600 ms prior to each target presentation. Anticipatory smooth eye velocity was assessed by calculating eye velocity 50 ms after target onset (V ₅₀), prior to the availability of visual feedback. Despite being required to re-fixate centre during inter-ramp gaps, subjects could still generate anticipatory smooth pursuit with V ₅₀ comparable to single speed control sequences, but with less accuracy. In the steady state V ₅₀ was appropriately scaled in proportion to upcoming target velocity for each ramp component and thus truly predictive. Only one to two repetitions were required to attain a steady-state for unidirectional sequences (four or six ramps), but three or four repeats were required for bi-directional sequences. Results suggest working memory can be used to acquire multiple levels of velocity information for prediction, but its use in rapid prediction is compromised when direction as well as speed must be retained.     

Stress-induced impairment of inhibitory avoidance learning in female neuromedin B receptor-deficient mice

Neuromedin B (NMB) is a mammalian bombesin (BN)-like peptide that exerts its function via the neuromedin B receptor (NMB-R). The NMB/NMB-R system is involved in stress response, and therefore we examined behavioral properties in female mice lacking NMB-R using a restraint-induced stress paradigm. Thirty minutes of restraint in a wire mesh cage constituted a sufficient stress stimulus for mice as evidenced by elevated blood glucose concentrations in stressed wild-type and NMB-R-deficient mice. Using a one-trial passive avoidance test, stressed NMB-R-deficient mice exhibited a marked reduction in memory performance. NMB-R-deficient mice exhibited elevated spontaneous activity in a novel environment compared to non-stressed mutant mice after 30-min stress, and a similar difference was also observed between stressed/non-stressed wild-type mice. An elevated plus maze test showed that the stress stimulus had no effect on anxiety in either wild-type or NMB-R-deficient mice. Furthermore, pain response of wild-type and NMB-R-deficient mice induced by electric foot shock was not affected under either stressed or non-stressed conditions. These results indicate that impaired memory performance in stressed NMB-R-deficient mice is not a consequence of changes in spontaneous activity, anxiety, or pain response, and suggest that the NMB/NMB-R pathway may play a role in regulating the stress response via the neural system that controls learning and memory.     

Absolute pitch and pupillary response: effects of timbre and key color

The pitch identification performance of absolute pitch possessors has previously been shown to depend on pitch range, key color, and timbre of presented tones. In the present study, the dependence of pitch identification performance on key color and timbre of musical tones was examined by analyzing hit rates, reaction times, and pupillary responses of absolute pitch possessors (n = 9) and nonpossessors (n = 12) during a pitch identification task. Results revealed a significant dependence of pitch identification hit rate but not reaction time on timbre and key color in both groups. Among absolute pitch possessors, peak dilation of the pupil was significantly dependent on key color whereas the effect of timbre was marginally significant. Peak dilation of the pupil differed significantly between absolute pitch possessors and nonpossessors. The observed effects point to the importance of learning factors in the acquisition of absolute pitch.     

Functional relation between corticonuclear input and movements evoked on microstimulation in cerebellar nucleus interpositus anterior in the cat

The functional relation between receptive fields of climbing fibres projecting to the C1, C3 and Y zones and forelimb movements controlled by nucleus interpositus anterior via the rubrospinal tract were studied in cats decerebrated at the pre-collicular level. Microelectrode tracks were made through the caudal half of nucleus interpositus anterior. This part of the nucleus receives its cerebellar cortical projection from the forelimb areas of these three sagittal zones. The C3 zone has been demonstrated to consist of smaller functional units called microzones. Natural stimulation of the forelimb skin evoked positive field potentials in the nucleus. These potentials have previously been shown to be generated by climbing fibre-activated Purkinje cells and were mapped at each nuclear site, to establish the climbing fibre receptive fields of the afferent microzones. The forelimb movement evoked by microstimulation at the same site was then studied. The movements usually involved more than one limb segment. Shoulder retraction and elbow flexion were frequently evoked, whereas elbow extension was rare and shoulder protraction never observed. In total, movements at the shoulder and/or elbow occurred for 96% of the interpositus sites. At the wrist, flexion and extension movements caused by muscles with radial, central or ulnar insertions on the paw were all relatively common. Pure supination and pronation movements were also observed. Movements of the digits consisted mainly of dorsal flexion of central or ulnar digits. A comparison of climbing fibre receptive fields and associated movements for a total of 110 nuclear sites indicated a general specificity of the input-output relationship of this cerebellar control system. Several findings suggested that the movement evoked from a particular site would act to withdraw the area of the skin corresponding to the climbing fibre receptive field of the afferent microzones. For example, sites with receptive fields on the dorsum of the paw were frequently associated with palmar flexion at the wrist, whereas sites with receptive fields on the ventral side of the paw and forearm were associated with dorsiflexion at the wrist. Correspondingly, receptive fields on the lateral side of the forearm and paw were often associated with flexion at the elbow, whereas sites with receptive fields on the radial side of the forearm were associated with elbow extension. The proximal movements that were frequently observed also for distal receptive fields may serve to produce a general shortening of the limb to enhance efficiency of the withdrawal. It has previously been suggested that the cerebellar control of forelimb movements via the rubrospinal tract has a modular organisation. Each module would consist of a cell group in the nucleus interpositus anterior and its afferent microzones in the C1, C3 and Y zones, characterised by a homogenous set of climbing fibre receptive fields. The results of the present study support this organisational principle, and suggest that the efferent action of a module is to withdraw the receptive field from an external stimulus. Possible functional interpretations of the action of this system during explorative and reaching movements are discussed.