Multiple causes of collaborative inhibition in memory for categorised word lists.

Collaborative inhibition is the finding that collaborative groups recall less information than nominal groups (the combined output of an equal number of individuals). The retrieval strategy disruption explanation of collaborative inhibition argues that individuals' idiosyncratic retrieval strategies are disrupted by hearing the contributions of others. In a series of studies, we investigated the role of retrieval interference and other cognitive explanations of collaborative inhibition. We asked collaborative and nominal dyads to recall lists of categorised words. We found that collaborative inhibition results from retrieval strategy disruption and from other factors. Collaborative dyads displayed more limited exploration than nominal dyads: They sampled from fewer categories and, thus, recalled fewer words. Collaborative dyads have different goals than nominal dyads, particularly limiting errors which may also reduce correct recall. We also found that the time period of recall contributes to collaborative inhibition because collaborative dyads recall fewer words early in the retrieval period but more words later than nominal dyads. In addition, we found instances of collaborative advantages such that collaborative dyads made fewer errors and demonstrated more recall organisation than nominal dyads.

Expression, purification, and enzymatic characterization of the dual specificity mitogen-activated protein kinase phosphatase, MKP-4.

Mitogen-activated protein kinase phosphatase-4 (MKP-4) is a dual specificity phosphatase, which acts as a negative regulator of insulin-stimulated pathways. Here, we describe expression, purification, and biochemical characterization of MKP-4. We used the Baculovirus expression system and purification with a combination of affinity and gel filtration chromatography to generate pure MKP-4 and MKP-4/p38 complex. Both MKP-4 and the MKP-4/p38 complex exhibited moderate activity toward the surrogate substrates p-nitrophenyl phosphate, 6, 8-difluoro-4-methylumbelliferyl phosphate, and 3-O-methylfluorescein phosphate. The phosphatase activity could be inhibited by peroxovanate, a potent inhibitor of protein tyrosine phosphatases. We further determined kinetic parameters for the MKP-4 and the MKP-4/p38 by using spectrophotometric and fluorescence intensity methods. The MKP-4/p38 complex was found to provide substantially higher phosphatase activity than MKP-4 alone, similar to what has been shown for MKP-3. Our data allow the configuration of screens for modulators of MKP-4 activity.