Lack of the metabotropic glutamate receptor subtype 7 selectively modulates Theta rhythm and working memory

Metabotropic glutamate receptors (mGluRs) are known to play a role in synaptic plasticity and learning. We have previously shown that mGluR7 deletion in mice produces a selective working memory (WM) impairment, while other types of memory such as reference memory remain unaffected. Since WM has been associated with Theta activity (6-12 Hz) in EEGs, and since EEG abnormalities have been observed in these mice before, we studied the effect of mGluR7 gene ablation on EEG activity in the hippocampus, in particular in the Theta range, during performance of a WM task. In an eight-arm maze with four arms baited, mGluR7 knock-out (KO) and wild-type mice committed the same number of reference memory errors, whereas KOs committed more WM errors. While performing the task, KO mice showed substantially higher Theta amplitudes, and the ratio of Theta to overall EEG power was much increased. No change was seen in the Delta (0-5 Hz), or Gamma (30-40 Hz) EEG bands compared with controls. When recording EEGs during periods of rest in the home cages, no difference was seen between groups. These findings suggest that mGluR7 is important for modulation and control of Theta activity. Since only WM was affected, and only the Theta range of EEG activity was altered, these results show a correlation between Theta rhythm and WM performance, and therefore support the concept that Theta activity in the hippocampus is involved in WM storage.     

Effects of the presence of others on food intake: a normative interpretation

The authors review the effect of the presence of others on food intake. In social facilitation studies, people tend to eat more in groups than when alone. In modeling studies, the presence of others may facilitate or inhibit intake, depending on how much these other people eat. Studies of impression management demonstrate that people tend to eat less in the presence of others than when alone. The authors attempt to reconcile these divergent literatures by reference to a model of inhibitory norms that govern eating. In the presence of palatable food, and in the absence of clear signals of satiety, people look outward to cues from the environment to determine when to stop eating. Socially derived inhibitory norms can account for either increased or decreased intake in the presence of others, depending on how much the others eat and the extent to which one is eager to impress them.     

Speech errors, disfluencies, and self-repairs of stutterers in two accuracy conditions

The purpose of the present study was to see whether the covert repair hypothesis, which views normal disfluencies as the by-products of covert self-repairing of internal speech (programming) errors, applies to habitual stutterers. To this end, we examined the effects of emphasis on speech accuracy in stutterers on three sorts of incidents: speech errors, disfluencies (also including stuttering), and self-repairs. In a condition in which they performed a speech task under instructions stressing the accuracy of speaking, stutterers made considerably fewer speech errors, than in a condition in which speech accuracy could be ignored. On the other hand, disfluency and self-repair rates remained about the same. They did increase, however, relative to speech error rates with accuracy emphasis. A control group of normal speakers performed in a similar way. Apparently, disfluencies behaved like self-repairs. These results support the covert repair hypothesis of disfluency, both for stutterers and for normal speakers.     

The development of cognitive mapping of the large-scale environment

Two experiments were conducted to investigate the development of children's cognitive maps of large-scale environments. Kindergarten (Mean Age = 5?7), second (Mean Age = 7?7), and fifth (Mean Age = 10?7) graders walked through a large model town and were then required to construct the layout of building in that model from memory. Accuracy of construction increased as a function both of developmental level and repeated encounters with the layout. In Experiment 1, the separate effects of repeatedly walking through the town and repeatedly constructing it both increased the accuracy of the children's reconstructions. In Experiment 2, walking through the environment was no more effective than merely viewing it repeatedly. Young children's accuracy in bounded space (Experiment 1) was far more accurate than their performance in unbounded space (Experiment 2), while older children's accuracy was relatively unaffected by this variable.     

Visual word recognition of three-letter words as derived from the recognition of the constituent letters

Word recognition is one of the basic processes involved in reading. In this connection, a model for word recognition is proposed consisting of a perceptual and a decision stage. It is supposed that, in the perceptual stage, the formation of possible words proceeds by separate identification of each of the letters of the stimulus word in their positions. Letter perception is taken to be conditional on position because of interaction effects from neighboring letters. These effects are dependent on both position in the word and retinal eccentricity, which are of particular relevance in reading. The letter-based approach rests on the strong relationship between the results from single-letter recognition in meaningless strings and in real words. Next, in the decision step, the many alternatives generated in the perceptual stage are matched with a vocabulary of real words. It is supposed that the final choice from among the remaining words is made in accordance with the constant ratio rule; frequency effects are not separately incorporated in the model. All predictions of the model are generated by means of data from earlier experiments. Despite being not optimally suited for this purpose, the predictions compare favorably with responses in word-recognition experiments.     

Performance of retarded adolescents and nonretarded children on one- and two-bit logical problems

Groups of adolescents of retarded and borderline intelligence, ranging in IQ from 44 to 80 and in mean MA (mental age) from 8 to 12 yr, and groups of nonretarded children ranging in mean MA from 6 to 12 yr, were given logical problem solving tasks. In the nonretarded groups, on a one-bit problem only the kindergarten children (mean MA = 6 yr) failed to perform above chance, and were not tested further. On a two-bit problem, only the first graders (mean MA = 7 yr) failed to perform above chance.Conversely, in the low IQ groups, only the borderline group (mean MA = 12 yr) performed reliably above chance on the one-bit problem, and none performed above chance on the two-bit problem. There is a profound deficiency in low IQ individuals on certain tasks requiring logic and foresight, and MA markedly over-estimates their performance relative to the performance of nonretarded individuals.