Brain research. Cognitive brain research最新文献

Lanthanum chloride (5.0 mM) administered immediately after a visual reminder presented to day-old chickens between 7.5 min and 48 h following a single trial passive avoidance learning task produced an immediate but transient loss of memory on retention test, an effect not observed in the absence of a reminder. The duration of the transient deficit was relatively stable with lanthanum chloride consistently inducing a loss of memory that was evident 5 min after the reminder, with recovery by 10-15 min. The results suggest that, for a period of at least up to 48 h after passive avoidance training, the activation of memory retrieval by a reminder stimulus may lead to processes which are sensitive to inhibition by the calcium channel antagonist lanthanum chloride. These results extend previously reported findings implicating the involvement of glutamate-sensitive channels in a transient memory process that is also activated as a result of a reminder stimulus, but that is no longer present 48 h after training. The glutamate-sensitive mechanism appears to be a secondary mechanism activated following memory retrieval and to be dependent on the level of memory consolidation that the memory for the original experience has undergone. The results presented here suggest that lanthanum chloride, a calcium channel antagonist, inhibits memory retrieval in the day-old chick. This effect implicates calcium channel mediated processes in immediate memory recall. Further, the results suggest the lanthanum inhibits a primary mechanism, that precedes that glutamate-sensitive mechanism identified previously and that both are dependent on the activation of memory retrieval by a reminder.

Within the theoretical framework of reference, the brain errs in processing complex stimuli, such as faces. Thus, these stimuli not only activate accurate representations but also inaccurate representations corresponding to known persons who resemble the face stimulus, and hence knowledge about these known persons. Since more errors are made in processing unfamiliar than familiar stimuli, these inaccurate activations are assumed to be more frequent, and/or more intense, with unknown than with known faces. Moreover, top-down mechanisms favor representations of stimuli that are congruent with the context, and representations of known persons, even if inaccurate, receive an additional amount of activation in contexts wherein known faces are expected. Inaccurate representations have to be inhibited to achieve accurate recognition. Thus, more inhibition would be required for unknown than for known faces, and in contexts wherein known faces are expected. The aim of the present work is to study the hypothesis that the N400 component of the event-related potentials (ERPs) reflects the inhibition of knowledge, and to see whether this hypothesis accounts for the N400-like potential elicited by faces. To achieve that goal, ERPs to known and unknown faces were recorded while the richness in known faces of each experimental block, and thus the expectancy for known faces, was manipulated. Consistent with the hypothesis, the amplitudes of the N400-like components were greater in conditions where more inhibition was required, i.e. for unknown rather than for known faces, and in the context of the block rich in known faces. This context effect was larger for unknown than for faces, and in the context of the block rich in known faces. This context effect was larger for unknown than for known faces.

In a patient affected by locked-in syndrome, because of a lesion of the caudal-ventral pontine tegment, we recorded event-related potentials (ERPs) to an acoustic odd-ball paradigm. We did not record N2 and P3 components in the 50 days following the acute lesion although the patient was able to understand the task and communicate with blinking. 55 days after the acute lesion, N2 and P3 reappeared on scalp derivations. This findings suggest that brainstem structures are involved in P3 or N2-P3 generation.