Verbal instructions and top-down saccade control.

Few studies have addressed the interaction between instruction content and saccadic eye movement control. To assess the impact of instructions on top-down control, we instructed 20 healthy volunteers to deliberately delay saccade triggering, to make inaccurate saccades or to redirect saccades--i.e. to glimpse towards and then immediately opposite to the target. Regular pro- and antisaccade tasks were used for comparison. Bottom-up visual input remained unchanged and was a gap paradigm for all instructions. In the inaccuracy and delay tasks, both latencies and accuracies were detrimentally impaired by either type of instruction and the variability of latency and accuracy was increased. The intersaccadic interval (ISI) required to correct erroneous antisaccades was shorter than the ISI for instructed direction changes in the redirection task. The word-by-word instruction content interferes with top-down saccade control. Top-down control is a time consuming process, which may override bottom-up processing only during a limited time period. It is questionable whether parallel processing is possible in top-down control, since the long ISI for instructed direction changes suggests sequential planning.

Hemispheric asymmetry in visuospatial attention assessed with transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) was used to study visuospatial attention processing in ten healthy volunteers. In a forced choice recognition task the subjects were confronted with two symbols simultaneously presented during 120 ms at random positions, one in the left and the other in the right visual field. The subject had to identify the presented pattern out of four possible combinations and to press the corresponding response key within 2 s. Double-pulse TMS (dTMS) with a 100-ms interstimulus interval (ISI) and an intensity of 80% of the stimulator output (corresponding to 110-120% of the motor threshold) was applied by a non-focal coil over the right or left posterior parietal cortex (PPC, corresponding to P3/P4 of the international 10-20 system) at different time intervals after onset of the visual stimulus (starting at 120 ms, 270 ms and 520 ms). Double-pulse TMS over the right PPC starting at 270 ms led to a significant increase in percentage of errors in the contralateral, left visual field (median: 23% with TMS vs 13% without TMS, P=0.0025). TMS applied earlier or later showed no effect. Furthermore, no significant increase in contra- or ipsilateral percentage of errors was found when the left parietal cortex was stimulated with the same timing. These data indicate that: (1) parietal influence on visuospatial attention is mainly controlled by the right lobe since the same stimulation over the left parietal cortex had no significant effect, and (2) there is a vulnerable time window to disturb this cortical process, since dTMS had a significant effect on the percentage of errors in the contralateral visual hemifield only when applied 270 ms after visual stimulus presentation.

Double-pulse transcranial magnetic stimulation over the frontal eye field facilitates triggering of memory-guided saccades.

The study investigated the influence of double-pulse transcranial magnetic stimulation (dTMS) on memory-guided saccade triggering. Double pulses with interstimulus intervals (ISIs) of 35, 50, 65 or 80 ms were applied over the right frontal eye field (FEF) and as control over the occipital cortex. A significant dTMS effect was found exclusively for contralateral saccades; latency of memory-guided saccades was reduced after FEF stimulation with an ISI of 50 ms compared to latency without stimulation. This effect proved to be specific for the ISI of 50 ms over the FEF because control stimulation with the same ISI over the occipital cortex had no significant effect on latency of memory-guided saccades. The results of our study showed that, by using an appropriate ISI, dTMS is able to facilitate contralateral saccade triggering by stimulating the FEF. This suggests that TMS interferes specifically with saccade triggering mechanisms, probably by acting on presaccadic neurons of the FEF.

Weber fractions and time-order errors for long and short durations: Implications for modeling

Using a weighted up-down procedure, in each of eight conditions 28 participants compared durations of auditory (noise bursts) or visual (LED flashes) intervals; filled or unfilled with 3-ms markers; with or without feedback. Standards (Sts) were 100 and 1000 ms, and the ISI 900 ms. Intermixedly, presentation orders were St-Comparison (Co) and Co-St. TOEs were positive for St=100-ms and negative for St=1000 ms. Weber fractions (WFs, JND/St) were lowered by feedback. For visual-filled and visual-empty, WFs were highest for St=100 ms. For auditory-filled and visual-empty, St interacted with Order: lowest WFs occurred for St-Co with St=1000 ms, but for Co-St with St=100 ms. Lowest average WFs occurred with St-Co for visual-filled, but with Co-St for visual-empty. The results refute the generalization of better discrimination with St-Co than with Co-St (”type-B effect”), and support the notion of sensation weighting: flexibly differential impact weights of the compared durations in generating the response.

The Hundred Most-Cited Publications in Orthopaedic Knee Research

BACKGROUND: Despite its limitations, citation analysis remains one of the best currently available tools for quantifying the impact of articles. Bibliometric studies list the "best-sellers" in a single location, and they have been published frequently in many fields during recent years. The purpose of the present study was to report the qualities and characteristics of citation classics in orthopaedic knee research. METHODS: The database of the Institute for Scientific Information (ISI) was utilized for identification of articles published from 1945 to March 2014. All knee articles that had been published in sixty-five orthopaedic and twenty-nine rheumatology journals and that had been cited at least 200 times were identified. The top 100 were selected for further analysis of authorship, source journal, number of citations, citation rate (both since publication and in 2013), geographic origin, article type, and level of evidence. RESULTS: The publication dates of the 100 most-cited articles ranged from 1948 to 2007, with the greatest number of articles published in the 1980s. Citations per article ranged from 2640 to 287. All articles were published in eleven of the ninety-four journals. The leading countries of origin were the U.S. followed by the U.K. and Sweden. The two main focus areas were sports traumatology and degenerative disease. The number of citations per article was also greatest for articles published in the 1980s. Basic research articles were cited more quickly, but not more often, than clinical articles. Most articles represented Level-IV evidence, followed by Levels II, III, and I. CONCLUSIONS: This bibliometric study is likely to include a list of intellectual milestones in orthopaedic knee research. It is apparent that a high level of evidence is not mandatory for an article to gain a large number of citations. Bibliometric reports provide a reflection of the quality of cited research published in a specific field and should therefore provoke thinking within the scientific community.

Is mental practice an effective adjunct therapeutic strategy for upper limb motor restoration after stroke?

Stroke is one of the most common conditions requiring rehabilitation, and its motor impairments are a major cause of permanent disability. Hemiparesis is observed by 80% of the patients after acute stroke. Neuroimaging studies showed that real and imagined movements have similarities regarding brain activation, supplying evidence that those similarities are based on the same process. Within this context, the combination of MP with physical and occupational therapy appears to be a natural complement based on neurorehabilitation concepts. Our study seeks to investigate if MP for stroke rehabilitation of upper limbs is an effective adjunct therapy. PubMed (Medline), ISI knowledge (Institute for Scientific Information) and SciELO (Scientific Electronic Library) were terminated on 20 February 2015. Data were collected on variables as follows: sample size, type of supervision, configuration of mental practice, setting the physical practice (intensity, number of sets and repetitions, duration of contractions, rest interval between sets, weekly and total duration), measures of sensorimotor deficits used in the main studies and significant results. Random effects models were used that take into account the variance within and between studies. Seven articles were selected. As there was no statistically significant difference between the two groups (MP vs Control), showed a – 0.6 (95% CI: –1.27 to 0.04), for upper limb motor restoration after stroke. The present meta-analysis concluded that MP is not effective as adjunct therapeutic strategy for upper limb motor restoration after stroke.

Making regression tables from stored estimates

Organizing and archiving statistical results and processing a subset of those results for publication are important and often underestimated issues in conducting statistical analyses. Because automation of these tasks is often poor, processing results produced by statistical packages is quite laborious and vulnerable to error. I will therefore present a new package called estout that facilitates and automates some of these tasks. This new command can be used to produce regression tables for use with spreadsheets, LaTeX, HTML, or word processors. For example, the results for multiple models can be organized in spreadsheets and can thus be archived in an orderly manner. Alternatively, the results can be directly saved as a publication-ready table for inclusion in, for example, a LaTeX document. estout is implemented as a wrapper for estimates table but has many additional features, such as support for mfx. However, despite its flexibility, estout is—I believe—still very straightforward and easy to use. Furthermore, estout can be customized via so-called defaults files. A tool to make available supplementary statistics called estadd is also provided.

Random Sampling with Interspike-Intervals of the Exponential Integrate and Fire Neuron: A Computational Interpretation of UP-States

Oscillations between high and low values of the membrane potential (UP and DOWN states respectively) are an ubiquitous feature of cortical neurons during slow wave sleep and anesthesia. Nevertheless, a surprisingly small number of quantitative studies have been conducted only that deal with this phenomenon’s implications for computation. Here we present a novel theory that explains on a detailed mathematical level the computational benefits of UP states. The theory is based on random sampling by means of interspike intervals (ISIs) of the exponential integrate and fire (EIF) model neuron, such that each spike is considered a sample, whose analog value corresponds to the spike’s preceding ISI. As we show, the EIF’s exponential sodium current, that kicks in when balancing a noisy membrane potential around values close to the firing threshold, leads to a particularly simple, approximative relationship between the neuron’s ISI distribution and input current. Approximation quality depends on the frequency spectrum of the current and is improved upon increasing the voltage baseline towards threshold. Thus, the conceptually simpler leaky integrate and fire neuron that is missing such an additional current boost performs consistently worse than the EIF and does not improve when voltage baseline is increased. For the EIF in contrast, the presented mechanism is particularly effective in the high-conductance regime, which is a hallmark feature of UP-states. Our theoretical results are confirmed by accompanying simulations, which were conducted for input currents of varying spectral composition. Moreover, we provide analytical estimations of the range of ISI distributions the EIF neuron can sample from at a given approximation level. Such samples may be considered by any algorithmic procedure that is based on random sampling, such as Markov Chain Monte Carlo or message-passing methods. Finally, we explain how spike-based random sampling relates to existing computational theories about UP states during slow wave sleep and present possible extensions of the model in the context of spike-frequency adaptation.

"Das Judenproblem und seine Lösung" [Rezension]

Isi Kahn

Cerebellar mechanisms for motor learning: Testing predictions from a large-scale computer simulation

The cerebellum is the major brain structure that contributes to our ability to improve movements through learning and experience. We have combined computer simulations with behavioral and lesion studies to investigate how modification of synaptic strength at two different sites within the cerebellum contributes to a simple form of motor learning—Pavlovian conditioning of the eyelid response. These studies are based on the wealth of knowledge about the intrinsic circuitry and physiology of the cerebellum and the straightforward manner in which this circuitry is engaged during eyelid conditioning. Thus, our simulations are constrained by the well-characterized synaptic organization of the cerebellum and further, the activity of cerebellar inputs during simulated eyelid conditioning is based on existing recording data. These simulations have allowed us to make two important predictions regarding the mechanisms underlying cerebellar function, which we have tested and confirmed with behavioral studies. The first prediction describes the mechanisms by which one of the sites of synaptic modification, the granule to Purkinje cell synapses (gr → Pkj) of the cerebellar cortex, could generate two time-dependent properties of eyelid conditioning—response timing and the ISI function. An empirical test of this prediction using small, electrolytic lesions of the cerebellar cortex revealed the pattern of results predicted by the simulations. The second prediction made by the simulations is that modification of synaptic strength at the other site of plasticity, the mossy fiber to deep nuclei synapses (mf → nuc), is under the control of Purkinje cell activity. The analysis predicts that this property should confer mf → nuc synapses with resistance to extinction. Thus, while extinction processes erase plasticity at the first site, residual plasticity at mf → nuc synapses remains. The residual plasticity at the mf → nuc site confers the cerebellum with the capability for rapid relearning long after the learned behavior has been extinguished. We confirmed this prediction using a lesion technique that reversibly disconnected the cerebellar cortex at various stages during extinction and reacquisition of eyelid responses. The results of these studies represent significant progress toward a complete understanding of how the cerebellum contributes to motor learning. ^

Na 1 Nachlass Max Horkheimer, 19 - Korrespondenzen u.a. mit Alfred Haas (p. I 10, 1-250)

20 Briefe zwischen Alfred Haas und Max Horkheimer, 1935-1941; 2 Briefe von Willy Haas an Max Horkheimer, 1938; 3 Briefe zwischen Virginia Haber und Max Horkheimer, 12.09.1945, August 1945; 7 Briefe zwischen Hugo Hahn und Max Horkheimer, 1942-1946; 1 Brief von Max Horkheimer an Charles G. Haines, 23.10.1940; 1 Brief von Max Horkheimer an Hall, 02.07.1939; 2 Briefe zwischen H. Duncan Hall und Max Horkheimer, 04.08.1939, 24.07.1939; 2 Briefe zwsichen Herbert Berkerath und Max Horkheimer, 10.10.1939, 09.10.1939; 23 Briefe zwischen Wolfgang Hallgarten und Max Horkheimer, 1937-1941; 1 Brief von Max Horkheimer an die American Philosophic Society Philadelphia, 15.04.1940; 2 Briefe zwischen Betty Drury und Max Horkheimer, 29.02.1940, 20.02.1940; 6 Briefe zwischen Nina Almond und Max Horkheimer, 1939; 1 Brief von Ruth E. Hollander an Max Horkheimer, 08.09.1938; 1 Brief von dem Brooklyn College an Wolfgang Hallgarten, 29.04.1938; 4 briefe zwischen dem Brooklyn College und Max Horkheimer, 18.05.1938, 17.05.1938; 2 Briefe zwischen Robert Maynard Hutchins und Max Horkheimer, 02.11.1937, 28.10.1937; 2 Briefe zwsichen Hardt und Max Horkheimer, 01.10.1943; 4 Briefe zwischen Gertrude Hardt und Max Horkheimer, 1947-1948; 4 Briefe zwischen den Harper & Brothers New York und Max Horkheimer, 24.10.1950, 1950; 1 Brief von Friedrich Pollock an Margot von Mendelssohn, 13.09.1950; 1 Brief von Hartoch an Max Horkheimer, 09.06.1937; 4 Briefe zwischen dem Harvard College Cambridge Massachusetts und Max Horkheimer, 1939-1940; 3 Briefe zwischen Felix Hase und Max Horkheimer, 1936, 13.03.1936; 1 Brief von Freda E. Hecht an Max Horkheimer, 01.03.1947; 1 Brief von Ernest S. Hediger an Max Horkheimer, 02.09.1940; 2 Briefe zwischen Agnes Heilbut und Max Horkheimer, 18.07.1938,; 7 Briefe zwischen Eduard Heimann und Max Horkheimer, 1936-1939; 1 Brief von Fritz Hein an Max Horkheimer, 14.06.1949; 2 Briefe zwischen Walter Heinemann und Max Horkheimer, 15.02.1945, 12.03.1945; 2 Briefe zwischen Philipp Heller und Max Horkheimer, 16.09.1944, 09.10.1944; 1 Brief von Max Horkheimer an Hellmann, 23.03.1939; 4 Briefe zwischen L. E. Hellmann und Max Horkheimer, 1939; 4 Briefe zwischen P. A. Hemerijk und Max Horkheimer, 1936-1937, 03.02.1936; 5 Briefe zwischen Carl G. Hempel und Max Horkheimer, 1939-1941; 1 Lebenslauf von Hans Henning; 1 Brief von Else Henschke an Max Horkheimer, 24.07.1940; 1 Briefe von Isi Hepner an Max Horkheimer, 23.01.1941; 1 Brief von Leo Löwenthal an Isi Hepner, 03.02.1941; 1 Brief von Gertrude E. Herman anMax Horkheimer, 10.12.1949; 1 Brief von Wilhelm G. Hertz an Max Horkheimer, 29.09.1938; 2 Briefe zwischen Wieland Herzfelde und der National City Bank of New York, 28.11.1939, 30.11.1939; 2 Briefe zwischen Karl Hess und Max Horkheimer, 14.08.1935, 25.10.1934; 4 Briefe zwischen Karl Heymann und Max Horkheimer, 1947, 1949; 19 Briefe zwischen Robert Hilb und Max Horkheimer, 1937-1941; 2 Briefe zwischen Joseph Rosenthal und Max Horkheimer, 12.11.1940, 25.10.1940; 2 Briefe zwischen Henry Church und Max Horkheimer, 14.12.1940, 18.12.1940; 1 Brief von Ellen Hilb an Max Horkheimer, 11.03.1938; 1 Brief von Emil Hilb an Max Horkheimer, 15.04.1939; 2 Briefe zwischen Yoshitaro Hirano und Max Horkheimer, 1936, 23.01.1936; 2 Briefe von Max Horkheimer an Hirsch, 1938; 1 Brief von Arnold Hirsch an Max Horkheimer, 14.07.1949; 4 Briefe zwischen Charles Hirsch und Max Horkheimer, 1937, 1938; 2 Briefe von Max Horkheimer an Ernst Hirsch, Oktober 1938; 1 Brief von Max Horkheimer an Julius Hirsch, 24.02.1942;