Contrasting hippocampal and perirhinalcortex function using immediate early gene imaging

The perirhinal cortex and hippocampus have close anatomical links, and it might, therefore, be predicted that they have close, interlinked roles in memory. Lesion studies have, however, often failed to support this prediction, providing dissociations and double dissociations between the two regions on tests of object recognition and spatial memory. In a series of rat studies we have compared these two regions using the expression of the immediate early gene c-fosas a marker of neuronal activity. This gene imaging approach makes it possible to assess the relative involve-ment of different brain regions and avoids many of the limitations of the lesion approach. A very consistent pattern of results was found as the various hippocampal subfields but not the peri-rhinal cortex show increased c-fosactivity following tests of spatial learning. In contrast, the perirhinal cortex but none of the hippocampal subfields show increased c-fosactivity when presented with novel rather than familiar visual objects. When novel scenes are created by the spatial rearrangement of familiar objects it is the hippocampus and not the perirhinal cortex that shows c-foschanges. This double dissociation for gene expression accords with that found from lesion studies and highlights the different contributions of the perirhinal cortex and hippocampus to memory.     

Preconditions of predication: From qualia to quantum mechanics

Although in every inductive inference, an act of invention is requisite, the act soon slips out of notice. Although we bind together facts by superinducing upon them a new Conception, this Conception, once introduced and applied, is looked upon as inseparably connected with the facts, and necessarily implied in them. Having once had the phenomena bound together in their minds in virtue of the Conception men can no longer easily restore them back to the detached and incoherent condition in which they were before they were thus combined. The pearls once strung, they seem to form a chain by their nature. Induction has given them unity which it is so far from costing us an effort to preserve, that it requires an effort to imagine it dissolved — William Whewell, 1858. (Quoted from Butts (ed.), 1989, p. 143)     

Absence of priming coupled with substantially preserved recognition in lorazepam-induced amnesia

Two experiments are reported on priming when subjects are in an amnesic state induced by lorazepam. The primed tasks were completion of word-stems and generation of words from specified categories. In both experiments, lorazepam subjects showed no evidence of priming, whereas control subjects showed substantial priming. Recognition by the amnesic subjects of items produced in the priming tests, although impaired, was well above the chance level. These findings contrast with those obtained with organic amnesic subjects, for whom priming is typically normal but recognition is grossly impaired. The theoretical implications of this double dissociation between priming and recognition are discussed.