Hyperfamiliarity for faces

OBJECTIVE

To report 4 cases of hyperfamiliarity for faces (HFF) and review 5 previously reported cases.

METHODS

We identified cases of HFF from PubMed search and references in prior reports.

RESULTS

Three of our 4 cases had pathologic findings that were most extensive in the left temporal lobe. HFF occurred after a tonic-clonic seizure (cases 1 and 3), during simple partial seizures (case 2), and in the setting of an increase in simple partial seizure frequency but not during seizures (case 4). All 9 cases were adults with 1 or more seizures; symptoms first occurred after seizures in 5 cases and during seizures in 1 case. Ictal symptoms lasted from seconds to minutes and from 2 days to more than 7 years in the other 6 cases. The duration of HFF was not associated with the presence or extent of a structural lesion. While in several cases HFF appears to result from a postictal Todd paralysis, the mechanism underlying persistent cases is uncertain.

CONCLUSIONS

This modality (visual)-specific and stimulus (face)-specific syndrome is associated with diverse structural, functional imaging, and neurophysiologic findings. Lesions are more often left-sided and involve the temporal lobe. Epilepsy and seizures were present in all 9 cases, suggesting a pathophysiologic relationship, which likely varies among cases. Although only reported in 9 patients, HFF is probably much more common than it is diagnosed.

Category-specificity in the human medial temporal lobe cortex

The medial temporal lobe cortex (MTLC) occupies a pivotal position at the interface between neocortical association areas and the hippocampus. It has been suggested that the MTLC contains functionally distinct regions, with perirhinal cortex (PRc) preferentially supporting object processing and posterior parahippocampal cortex (PHc) preferentially supporting encoding of spatial information. Measuring differential BOLD responsiveness to objects, scenes, and other stimulus categories, we find a double dissociation between an anterior PRc response to objects and a posterior PHc response to scene stimuli. Furthermore, an anatomical ROI based approach was undertaken in an effort to understand the response profile underlying this double dissociation. We did not see any evidence for a sharp border between putatively distinct scene-preferential and object-preferential MTLC regions. Instead, scene-preferential responsiveness was noted to drop off in a graded, linear fashion in successively anterior MTLC regions until object-preferential responsiveness emerged in anterior PRc, although objects produced above baseline responses across the anterior-posterior extent of the parahippocampal gyrus. Other stimulus categories, such as faces and words, led to above baseline activation in either a few confined regions (faces) or none at all (words). Thus, what differentiated regions along the parahippocampal gryus was the relative response to objects and scenes, not simply above baseline responses to either category. This pattern raises the possibility that posterior PHc, and anterior PRc are situated at the ends of a single organizational continuum supported by the entire length of MTLC.

Content-specific source encoding in the human medial temporal lobe

Although the medial temporal lobe (MTL) is known to be essential for episodic encoding, the contributions of individual MTL subregions remain unclear. Data from recognition memory studies have provided evidence that the hippocampus supports relational encoding important for later episodic recollection, whereas the perirhinal cortex has been linked with encoding that supports later item familiarity. However, extant data also strongly implicate the perirhinal cortex in object processing and encoding, suggesting that perirhinal processes may contribute to later episodic recollection of object source details. To investigate this possibility, encoding activation in MTL subregions was analyzed on the basis of subsequent memory outcome while participants processed novel scenes paired with 1 of 6 repeating objects. Specifically, encoding activation correlating with later successful scene recognition memory was evaluated against that of source recollection for the object paired with the scene during encoding. In contrast to studies reporting a link between perirhinal cortex and item familiarity, it was found that encoding activation in the right perirhinal cortex correlates with successful recollection of the paired object. Furthermore, other MTL subregions also exhibited content-specific source encoding patterns of activation, suggesting that MTL subsequent memory effects are sensitive to stimulus category.

Cognitive neuroscience: forgetting of things past

Recent functional imaging and electrophysiological results indicate that failure to remember experiences can result from a decreased recruitment of encoding processes that build effective memories and an increased recruitment of alternative mechanisms that may impair effective learning.

When keeping in mind supports later bringing to mind: neural markers of phonological rehearsal predict subsequent remembering

The ability to bring to mind a past experience depends on the cognitive and neural processes that are engaged during the experience and that support memory formation. A central and much debated question is whether the processes that underlie rote verbal rehearsal-that is, working memory mechanisms that keep information in mind-impact memory formation and subsequent remembering. The present study used event-related functional magnetic resonance imaging (fMRI) to explore the relation between working memory maintenance operations and long-term memory. Specifically, we investigated whether the magnitude of activation in neural regions supporting the on-line maintenance of verbal codes is predictive of subsequent memory for words that were rote-rehearsed during learning. Furthermore, during rote rehearsal, the extent of neural activation in regions associated with semantic retrieval was assessed to determine the role that incidental semantic elaboration may play in subsequent memory for rote-rehearsed items. Results revealed that (a) the magnitude of activation in neural regions previously associated with phonological rehearsal (left prefrontal, bilateral parietal, supplementary motor, and cerebellar regions) was correlated with subsequent memory, and (b) while rote rehearsal did not--on average--elicit activation in an anterior left prefrontal region associated with semantic retrieval, activation in this region was greater for trials that were subsequently better remembered. Contrary to the prevalent view that rote rehearsal does not impact learning, these data suggest that phonological maintenance mechanisms, in addition to semantic elaboration, support the encoding of an experience such that it can be later remembered.

Primate rhinal cortex participates in both visual recognition and working memory tasks: functional mapping with 2-DG

The rhinal cortex in the medial temporal lobe has been implicated in object recognition memory tasks and indeed is considered to be the critical node in a visual memory network. Previous studies using the 2-deoxyglucose method have shown that thalamic and hippocampal structures thought to be involved in visual recognition memory are also engaged by spatial and object working memory tasks in the nonhuman primate. Networks engaged in memory processing can be recognized by analysis of patterns of activation accompanying performance of specifically designed tasks. In the present study, we compared metabolic activation of the entorhinal and perirhinal cortex during the performance of three working memory tasks [delayed response (DR), delayed alternation (DA), and delayed object alternation (DOA)] to that induced by a standard recognition memory task [delayed match-to-sample (DMS)] and a sensorimotor control task in rhesus monkeys. A region-of-interest analysis revealed elevated local cerebral glucose utilization in the perirhinal cortex in animals performing the DA, DOA, and DMS tasks, and animals performing the DMS task were distinct in showing a strong focus of activation in the lateral perirhinal cortex. No significant differences were evident between groups performing memory and control tasks in the entorhinal cortex. These findings suggest that the perirhinal cortex may play a much broader role in memory processing than has been previously thought, encompassing explicit working memory as well as recognition memory.

Prominence of direct entorhinal-CA1 pathway activation in sensorimotor and cognitive tasks revealed by 2-DG functional mapping in nonhuman primate

The trisynaptic pathway from entorhinal cortex to the hippocampus has long been regarded as the major route of information transfer underlying memory consolidation. Most physiological studies of this pathway involve recording from hippocampal slices. We have used both single- and double-label 2-deoxyglucose autoradiographic methods to image the pattern of activation in the hippocampal formation of 14 rhesus monkeys performing cognitive tasks, varying in content (spatial or nonspatial), process (working memory or associative memory), and mode of response (oculomotor or manual). These studies revealed a highly differentiated pattern of metabolic activation throughout the rostrocaudal extent of the hippocampal formation that was common to all behavioral conditions examined. This pattern consisted of intense activation of the stratum lacunosum-moleculare of CA1 and the subiculum, contrasting with barely detectable activity in CA3 and modest activation in the dentate gyrus, which did not include its molecular layer. These findings indicate a remarkable invariance in hippocampal activation under conditions of varied content, varied process, and varied mode of response and an heretofore-unappreciated preferential engagement of the direct rather than the trisynaptic pathway during performance of a wide range of behavioral tasks.

A robust point-matching algorithm for autoradiograph alignment

We present a novel method for the geometric alignment of autoradiographs of the brain. The method is based on finding the spatial mapping and the one-to-one correspondences (or homologies) between point features extracted from the images and rejecting non-homologies as outliers. In this way, we attempt to account for the local, natural and artifactual differences between the autoradiograph slices. We have used the resulting automated algorithm on a set of left prefrontal cortex autoradiograph slices, specifically demonstrated its ability to perform point outlier rejection, validated its robustness property using synthetically generated spatial mappings and provided an anecdotal visual comparison with the well-known iterated closest-point (ICP) algorithm. Visualization of a stack of aligned left prefrontal cortex autoradiograph slices is also provided.

Differential activation of the caudate nucleus in primates performing spatial and nonspatial working memory tasks

The caudate nucleus is part of an anatomical network subserving functions associated with the dorsolateral prefrontal cortex (DLPFC). The aim of the present study was to investigate whether the metabolic activity in the striatum reflects specific changes in working memory tasks, which are known to be dependent on the DLPFC, and whether these changes reflect the topographic ordering of prefrontal connections within the striatum. Local cerebral glucose utilization (LCGU) rates were assessed in the striatum by the 14C-2-deoxyglucose method in monkeys that performed a spatial (delayed spatial alternation), a nonspatial (delayed object alternation) visual working memory task, or tasks that did not involve working memory, i.e., a visual pattern discrimination or sensorimotor paradigm. The results show a topographic segregation of activation related to spatial and nonspatial working memory, respectively. The delayed spatial alternation task increases LCGU rates bilaterally by 33-43% in the head of the caudate nucleus, where efferents from the dorsolateral prefrontal cortex project most densely. The delayed object alternation task enhances LCGU rates bilaterally by 32-37% in the body of the caudate nucleus, which is innervated by the temporal cortex. The visual pattern discrimination task similarly activated the body of the caudate, but in a smaller region and only in the right hemisphere. These findings provide the first evidence for metabolic activation of the caudate nuclei in working memory, supporting the role of this nucleus as a node in a neural network mediating DLPFC-dependent working memory processes. The double dissociation of activation observed suggests an anatomical and functional segregation of cortico-striatal circuits subserving spatial and nonspatial cognitive operations.

U50,488 increases ultrasonic vocalizations in 3-, 10-, and 18-day-old rat pups in isolation and the home cage

Separation-induced calling in the young of many species can be modulated by the opioid system. Morphine reduces ultrasonic vocalizations (USVs) produced by isolated rat pups, an effect blocked by naltrexone. Central administration of the mu and delta opiate receptor agonists DAMGO and DPDPE reduce USV; kappa receptor agonist U50,488 increases them. We now find that peripheral U50,488 not only boosted calling rates in isolated 3-, 10-, and 18-day-old rat pups, but also induced calling in pups of these ages tested in the home cage with their littermates, where USVs are seldom heard in nature. U50,488 lowered rectal temperature, although temperature loss and USV were not correlated within drug treatment groups.