The mismatch negativity (MMN) is an ERP component seen in response to unexpected “novel” stimuli, such as in an auditory oddball task. The MMN is of wide interest and application, but the neural responses that generate it are poorly understood. This is in part due to differences in design and focus between animal and human oddball paradigms. For example, one of the main explanatory models, the “predictive error hypothesis”, posits differences in timing and selectivity between signals carried in auditory and prefrontal cortex (PFC). However, these predictions have not been fully tested because (1) noninvasive techniques used in humans lack the combined spatial and temporal precision necessary for these comparisons and (2) single-neuron studies in animal models, which combine necessary spatial and temporal precision, have not focused on higher order contributions to novelty signals. In addition, accounts of the MMN traditionally do not address contributions from subcortical areas known to be involved in novelty detection, such as the amygdala. To better constrain hypotheses and to address methodological gaps between human and animal studies, we recorded single neuron activity from the auditory cortex, dorsolateral PFC, and basolateral amygdala of two macaque monkeys during an auditory oddball paradigm modeled after that used in humans. Consistent with predictions of the predictive error hypothesis, novelty signals in PFC were generally later than in auditory cortex and were abstracted from stimulus-specific effects seen in auditory cortex. However, we found signals in amygdala that were comparable in magnitude and timing to those in PFC, and both prefrontal and amygdala signals were generally much weaker than those in auditory cortex. These observations place useful quantitative constraints on putative generators of the auditory oddball-based MMN and additionally indicate that there are subcortical areas, such as the amygdala, that may be involved in novelty detection in an auditory oddball paradigm.

The aims of this study were to investigate whether patients with developmental amnesia (DA) associated with bilateral hippocampal volume reduction show an impairment in incidental nonverbal recall of action sequences, and whether the severity of this memory impairment is influenced by the sequence structure (causal vs. arbitrary). Like adult-onset cases of amnesia (McDonough, Mandler, McKee, & Squire, 1995), patients with DA did not differ significantly from their age-, sex-, and IQ-matched controls in spontaneous production of the sequences prior to modeling but recalled fewer target actions and action pairs than the control group after a 24-hour delay, independent of sequence structure. Unlike the patients with adult-onset amnesia, however, the patients with DA showed some memory for both types of sequences after a 24-hour delay. This difference in severity of memory impairment might reflect differences in extent of pathology and/or age at injury.

We report the performance on recognition memory tests of Jon, who, despite amnesia from early childhood, has developed normal levels of performance on tests of intelligence, language, and general knowledge. Despite impaired recall, he performed within the normal range on each of six recognition tests, but he appears to lack the recollective phenomenological experience normally associated with episodic memory. His recall of previously unfamiliar newsreel event was impaired, but gained substantially from repetition over a 2-day period. Our results are consistent with the hypothesis that the recollective process of episodic memory is not necessary either for recognition or for the acquisition of semantic knowledge.

Primate extrastriate visual cortex is organized into an occipitotemporal pathway for object vision and an occipitoparietal pathway for spatial vision. Correlations between normalized regional cerebral blood flow values (regional divided by global flows), obtained using H 2 15 O and positron emission tomography, were used to examine functional associations among posterior brain regions for these two pathways in 17 young men during performance of a face matching task and a dot-location matching task. During face matching, there was a significant correlation in the right hemisphere between an extrastriate occipital region that was equally activated during both the face matching and dot-location matching tasks and a region in inferior occipitotemporal cortex that was activated more during the face matching task. The corresponding correlation in the left hemisphere was not significantly different from zero. Significant intrahemispheric correlations among posterior regions were observed more often for the right than for the left hemisphere. During dot-location matching, many significant correlations were found among posterior regions in both hemispheres, but significant correlations between specific regions in occipital and parietal cortex shown to be reliably activated during this spatial vision test were found only in the right cerebral hemisphere. These results suggest that (1) correlational analysis of normalized rCBF can detect functional interactions between components of proposed brain circuits, and (2) face and dot-location matching depend primarily on functional interactions between posterior cortical areas in the right cerebral hemisphere. At the same time, left hemisphere cerebral processing may contribute more to dot-location matching than to face matching.

We previously reported selective activation of regional cerebral blood flow (rCBF) in occipitotemporal cortex during a face matching task (object vision) and activation in superior parietal cortex during a dot-location matching task (spatial vision) in young subjects, The purpose of the present study was to determine the effects of aging on these extrastriate visual processing systems. Eleven young (mean age 27 ± 4 years) and nine old (mean age 72 ± 7 years) male subjects were studied. Positron emission tomographic scans were performed using a Scanditronix PC1024–7B tomograph and H 2 15 O to measure rCBF. To locate brain areas that were activated by the visual tasks, pixel-by-pixel difference images were computed between images from a control task and images from the face and dot-location matching tasks. Both young and old subjects showed rCBF activation during face matching primarily in occipitotemporal cortex, and activation of superior parietal cortex during dot-location matching. Statistical comparisons of these activations showed that the old subjects had more activation of occipitotemporal cortex during the spatial task and more activation of superior parietal cortex during the object task than did the young subjects. These results show less functional separation of the dorsal and ventral visual pathways in older subjects, and may reflect an age-related reduction in the processing efficiency of these visual cortical areas.