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R Rousseau

Publications and source records attributed to R Rousseau.

16 recordsLinked to original sources
PubMed1997

Complete nucleotide sequence of the new simian T-lymphotropic virus, STLV-PH969 from a Hamadryas baboon, and unusual features of its long terminal repeat.

A third type of primate T-lymphotropic virus, PTLV-L, with STLV-PH969 as a prototype, has recently been isolated from an African baboon (Papio hamadryas). Classification of this virus has been based on partial sequence analysis of cDNA from a virus-producing cell line, PH969. We obtained the complete nucleotide sequence of this virus with a proviral genome of 8,916 bp. All major genes, homologous in all human T-cell lymphotropic virus (HTLV)-related viruses, and their corresponding mRNAs, including appropriate splicing, were identified. One additional nonhomologous open reading frame in the proximal pX region is accessible for translation through alternative splicing. Sequence comparison shows that STLV-PH969 is equidistantly related to HTLV type 1 (HTLV-1) and HTLV-2. In all coding regions, the similarity tends to be the lowest between STLV-PH969 and HTLV-1. However, in the long terminal repeat (LTR) region, the lowest similarity was found between STLV-PH969 and HTLV-2. The U3-R and R-U5 boundaries of the STLV-PH969 LTR were experimentally determined at nucleotides 268 and 524, respectively. This 695-bp LTR is 60 and 73 bp shorter than the LTRs of HTLV-1 and HTLV-2, respectively, but its general organization is similar to the one found in the HTLV-bovine leukemia virus genus. In the long region between the polyadenylation signal and the poly(A) site, sequence similarity with the HTLV-1 Rex-responsive element (RexRE) core and secondary structure prediction suggest the presence of a RexRE. The presence of three 21-bp repeats is conserved within the U3 region of HTLV-1, HTLV-2, and BLV. Only two direct repeats with similarity to these Tax-responsive elements were found in the STLV-PH969 LTR, which might suggest differences in the Tax-mediated transactivation of this virus. We conclude that STLV-PH969 has all the genes and genomic regions to suggest a replication cycle comparable to that of HTLV-1 and HTLV-2.

Amino Acid Sequence↗
PubMed1996

[Fulminant encephalopathy due to Shigella flexneri].

BACKGROUND: In some rare cases, Shigella flexneri infection may be associated with fulminating encephatopathy. CASE REPORT: A 6-year-old girl was admitted with fever, diarrhea and consciousness abnormalities. Brain CT scan was normal. Shigella flexneri type 2 was isolated from the stools. Despite antibiotic therapy, the encephalopathy was lethal. Two siblings were also infected, the first with only diarrhea, the second with headache and mild consciousness abnormalities: both children had a favorable course. CONCLUSIONS: Shigella flexneri encephalopathy is associated with high mortality rate in developed countries. Presence of headache could be a poor prognostic factor.

Child↗
PubMed1996

Tapping sensitivity to processing in short-term memory.

This experiment examines the interference between tapping and searching in short-term memory (STM). In a concurrent processing condition, the subject first memorized a set of digits, and then executed a series of 17 taps separated by 2 s subjective time intervals. In each intertap interval, a probe was presented for comparison with the items in the memory set. The amount of processing in STM was varied from series to series by manipulating the number of items in the memory set. The results showed that mean duration and variability of intertap intervals increased proportionally with memory set size. This effect is explained by interference between processing in STM and the timing component of the tapping performance. Tapping sensitivity to memory load suggests that, under some conditions, variations in tapping performance are valid indicators of STM processing requirements of a concurrent primary task.

Adult↗
PubMed1996

The genomic structure of a new simian T-lymphotropic virus, STLV-PH969, differs from that of human T-lymphotropic virus types I and II.

A new simian T-lymphotropic virus, STLV-PH969, was recently isolated from a wild-born Hamadryas baboon. Previous analysis had revealed that it differs sufficiently from the other HTLV/STLVs to be considered a new type, provisionally designated primate T-lymphotropic virus-L. Here we analyse a 3850 bp cDNA fragment spanning the 3' part of the STLV-PH969 genome. The fragment encodes three major proteins: Env, Tax and Rex. Sequence comparison and phylogenetic analysis indicate that in general STLV-PH969 tends to be more closely related to HTLV-II than to HTLV-I, although separate gene regions might have evolved under different constraints. Detailed comparison of the Env, Tax and Rex proteins among the HTLV-I, -II and STLV-PH969 prototypes reveals that the amino acid sequence of each protein shows a preferential conservation of functionally important domains. RNA-PCR on cytoplasmic messengers demonstrated splicing between a splice donor site immediately downstream of the env start codon, and two splice acceptor sites identified in the pX region. The predominant spliced messenger encodes both Tax and Rex. The other messenger potentially encodes a new viral protein from the proximal part of the pX region that is similar in amino acid composition to p12I and p10xI of HTLV-I and HTLV-II respectively. This genomic organization of the proximal pX region of STLV-PH969 is different from that found in HTLV-I and HTLV-II. Therefore, the distinct classification of this virus can be justified, not only in terms of sequence divergence but also in terms of its different genomic structure.

Amino Acid Sequence↗
PubMed1996

Stop-reaction time and the internal clock.

In a stop-reaction-time (stop-RT) task, a subject is presented with a regular, isochronous sequence of brief signals separated by a constant time interval, or stimulus onset asynchrony (SOA). His/her task is to press a response key as fast as possible when the sequence stops. As the sequence unfolds, an internal representation of the SOA duration builds up. Stop-RT is assumed to be triggered when an internal clock, operating as an "alarm clock," reaches a time criterion. Criterion setting is contingent upon variability in the SOA's internal representation. In Experiment 1A, stop-RT was measured for isochronous sequences of brief tones, light flashes, and also sequences of tones and flashes presented in regular alternation (tone-light-tone ...). Stop-RT was a linear function of SOA duration (ranging from 250 to 1,000 msec), regardless of modality, supporting a "central-clock" hypothesis. On the other and, taken together, the results of Experiments 1A, 1B, 2, and 3 suggest that no internal representation of the bimodal (tone-light) SOA of alternating sequences builds up. Indeed, an alternating sequence is physically equivalent to two interlaced isochronous subsequences, one auditory and one visual. So, two internal representations, one for the auditory (tone-tone) and one for the visual (light-light) SOA, could build up, and two time criteria running "in parallel" could thus support stop-RT. To provide a critical test of parallel timing, stop-RT was measured for bimodal 5:3 polyrhythms formed by the superposition of auditory and visual isochronous sequences that had different SOA durations (Experiment 4). Parallel timing accounted for a large proportion of variance in polyrhythmic stop-RT data. Overall findings can be accounted for by assuming a functional architecture of an internal clock in which pulses emitted by a central pacemaker are available in parallel with two modality-specific switch-accumulator "timing modules."

Acoustic Stimulation↗
PubMed1994

Object permanence and working memory in cats (Felis catus).

Cats (Felis catus) find an object when it is visibly moved behind a succession of screens. However, when the object is moved behind a container and is invisibly transferred from the container to the back of a screen, cats try to find the object at or near the container rather than at the true hiding place. Four experiments were conducted to study search behavior and working memory in visible and invisible displacement tests of object permanence. Experiment 1 compared performance in single and in double visible displacement trials. Experiment 2 analyzed search behavior in invisible displacement tests and in analogs using a transparent container. Experiments 3 and 4 tested predictions made from Experiment 1 and 2 in a new situation of object permanence. Results showed that only the position changes that cats have directly perceived are encoded and activated in working memory, because they are unable to represent or infer invisible movements.

Animals↗
PubMed1993

Time estimation and concurrent nontemporal processing: specific interference from short-term-memory demands.

Previous studies have shown that the effect of concurrent nontemporal processing on time estimation may vary depending on the level of difficulty of the nontemporal task. This is commonly interpreted within the context of so-called distraction/interruption models of temporal processing, which propose that as concurrent task difficulty or complexity is increased, temporal processing receives less attention. We hypothesize that the effect of nontemporal processing does not depend on the level of difficulty as such, but rather on the extent to which the concurrent nontemporal task specifically involves processing in short-term memory. Four experiments were run in which the short-term memory requirements of concurrent tasks were systematically varied, although all of the tasks were of comparable levels of difficulty. In the first experiment, the effect of memory search on simultaneous temporal productions was proportional to the number of items to search. As with reaction time, produced intervals were shown to increase linearly with the number of items in the memorized set. In Experiment 2, a visual search involving some load on short-term memory interfered in the same way with time production, although to a lesser extent. The last two experiments showed that performing attention-demanding visual search tasks that did not involve short-term memory did not lengthen simultaneously produced time intervals. This suggests that interference of nontemporal processing on time processing may not be a matter of nonspecific general purpose attentional resources, but rather of concurrent short-term-memory processing demands.

Adult↗
PubMed1993

[Sensitivity and diagnostic value of mental load in a secondary task on tapping rate].

When executed concurrently with a primary task, finger tapping performance is commonly interpreted as an indication of the primary task mental workload. Higher load during tapping induces an increase in mean or variability of intertap intervals. Finger tapping sensitivity was tested with series of 13 taps at a tapping rate of one tap every two seconds. Concurrent primary task required subjects to search for a target item, presented after each tap, in a three digit memory set memorized before each series. Processing load was varied by including letter targets amongst positive and negative digit targets. Letter target recognition should require less processing than digit recognition. Results show mean intertap intervals for letter targets to be shorter than for negative digit targets. Furthermore, recognition of negative digit targets induces a longer mean intertap interval than positive targets. These data suggest that continuous finger tapping is a sensitive index of the mental workload originating from working memory processing requirements. However, analysis of practice data show that development of strategies at performing the dual task may mask the sensitivity of the finger tapping task.

Adult↗
PubMed1991

Judging the relative duration of multimodal short empty time intervals.

Three experiments address the cause of the different performance levels found in time discrimination of empty intervals with durations near 250 msec. Performance differed according to the kind of sensory modality that marked the intervals. With a procedure in which the type of marker was randomized from trial to trial, it was shown that variability of discrimination judgments could not be attributed entirely to the variability of the criterion on which a judgment was based. Such a randomization slightly affects discrimination but provokes a reorganization related to marker conditions of the probabilities of judging an interval to be short or long. Moreover, it was shown that within intramodal conditions, physical characteristics of markers influence the discrimination performances. To account for the results generated with different marker-type intervals at 250 msec, we propose that two types of processor may be involved in duration discrimination: one is specifically related to a given sensory modality, whereas the other is aspecific and responsible for discrimination of intermodal intervals.

Adolescent↗