Parahippocampal Lesions Research Articles

Transtentorial Approach to Parahippocampal Lesions: A Technically Challenging Approach for Preserving Temporal Lobe Structures

In this installment of the Neurosurgical Atlas Series for WORLD NEUROSURGERY, the authors examine the paramedian supracerebellar transtentorial (SCTT) approach as a means of accessing the basal posteromedial temporal lobe for both intradural and extradural lesions. While other approaches, such as the subtemporal, transtemporal, and transsylvian routes, are often used to reach this otherwise impervious region, all of them do so at the expense of supratentorial structural integrity. Despite the long and narrow working distance provided by the SCTT approach, the access it provides to critical, deep-seated regions with little to no associated morbidity makes it our preferred approach in these patients. In this work, we highlight the perioperative considerations for this procedure, discuss the technical nuances of all aspects of the operation, and provide discussion on the approach in the context of its evolution and alternatives.

Selective impairment of race perception after bilateral damage in the fusiform and parahippocampal gyri

AbstractAimAlthough a previous functional magnetic resonance imaging study showed that the fusiform and parahippocampal gyri respond differentially to faces of the same versus different races, it is not clear whether the cortical regions are involved in perception of race. We examined whether two brain‐damaged patients with bilateral fusiform and parahippocampal lesions were able to perceive race. We also examined whether perception of race depended on perception of facial morphology, such as convex and concave surfaces.MethodsOne patient (patient S) had a focal lesion in the fusiform and parahippocampal gyri, and showed no signs of prosopagnosia. The other patient (patient O) had more extensive lesions and did show prosopagnosia. The patients and nine normal controls participated in a psychophysical race classification task using grayscale pictures and luminance‐reversed pictures.ResultsIn patient S, whose lesion was limited to the fusiform and parahippocampal gyri, the perception of race was selectively impaired. In patient O, who had more extensive lesions, race perception was also impaired. Furthermore, their race perception was especially impaired when the facial images were presented in reversed luminance.ConclusionThe present study suggests that the fusiform and parahippocampal gyri are involved in perception of race and that perception of facial surface is involved in distinguishing between races.

Parahippocampal Corpora Amylacea

Corpora amylacea (CA) normally accumulate within perivascular, subpial, and subependymal astrocytic processes. CA are associated with a number of conditions including normal aging, hippocampal sclerosis associated with temporal lobe epilepsy, multiple sclerosis, Lafora-type progressive myoclonic epilepsy, and adult polyglucosan body disease. Reports of massive localized accumulation of CA in the brain outside of these conditions are rare. A 49-year-old woman, with a long-standing history of migraine headaches, presented to her primary care provider for increased headache duration. Brain magnetic resonance imaging (MRI) revealed a left parahippocampal lesion, suggestive of low-grade glioma. Given the MRI suggestive of left parahippocampal glioma, left-sided frontotemporal craniotomy was performed for resection of the lesion. Specimens obtained during the operation revealed focal high-density accumulation of CA with no evidence of neoplasm, ischemia, or hypoxic injury. This case illustrates the possibility that localized high-density CA accumulation can present as an intrinsic lesion on brain MRI. CA should be included in the differential diagnosis for patients presenting with brain MRI suggestive of nonenhancing space-occupying lesions.

Neocortical Activation of the Hippocampus during Sleep in Infant Rats

We recently reported that the majority of hippocampal neurons in newborn rats increase their activity in association with myoclonic twitches, which are indicative of active sleep. Because spindle bursts in the developing somatosensory neocortex occur in response to sensory feedback from myoclonic twitching, we hypothesized that the state-dependent activity of the newborn hippocampus arises from sensory feedback that sequentially activates the neocortex and then hippocampus, constituting an early form of neocortical-hippocampal communication. Here, in unanesthetized 5- to 6-d-old rats, we test this hypothesis by recording simultaneously from forelimb and barrel regions of somatosensory neocortex and dorsal hippocampus during periods of spontaneous sleep and wakefulness and in response to peripheral stimulation. Myoclonic twitches were consistently followed by neocortical spindle bursts, which were in turn consistently followed by bursts of hippocampal unit activity; moreover, spindle burst power was positively correlated with hippocampal unit activity. In addition, exogenous stimulation consistently evoked this neocortical-to-hippocampal sequence of activation. Finally, parahippocampal lesions that disrupted functional connections between the neocortex and hippocampus effectively disrupted the transmission of both spontaneous and evoked neocortical activity to the hippocampus. These findings suggest that sleep-related motor activity contributes to the development of neocortical and hippocampal circuits and provides a foundation on which coordinated activity between these two forebrain structures develops.

Spatial Recognition in Cats: Effects of Parahippocampal Lesions

The role of the posterior parahippocampal area of the brain in spatial types of memory in conditions of one-trial visual perception of the positions of objects was studied by training eight cats to remember the spatial positions of either two different objects covering two of three feeders placed on a test tray (tests for the "object-place" association) or the positions of two of three feeders (tests for place). Each trial used new objects and new positions for the two of three feeders. After training, four cats were subjected to electrolytic lesioning of the posterior parahippocampal area, primarily the parahippocampal cortex, parasubiculum, and presubiculum; the remaining four cats underwent all the surgical procedures except electrocoagulation of nervous tissue; this was the sham-operated control group. Cats of this group showed no impairment to the performance of tests of both types, while the experimental group showed similar levels of impairment to the performance of both tests. Thus, memory for one-trial perception of "object-place" associations and, more simply, two different object places in cats were critically dependent on the posterior parahippocampal area.

Splenium or parahippocampus involvement and its relationship to cognitive decline in posterior cerebral artery infarction

Although cognitive impairment after a posterior cerebral artery (PCA) infarct is frequently observed, the important functional areas associated with cognitive decline, other than the thalamus, have not been determined. We investigated the locus or loci that might induce cognitive decline after a PCA infarct. Forty-one patients with unilateral PCA infarctions involving only the occipital lobe or the occipital lobe plus other PCA areas were included. All subjects received a mini-mental status examination (MMSE) within 2 months of onset; 43.9% had cognitive impairment. The severity of cognitive impairment was not associated with left hemisphere lesion location, sex, age, education level, or the time between stroke and the MMSE assessment. Only the lesion volume was negatively correlated with MMSE score. Lesion location analysis revealed that an occipital plus splenial or parahippocampal lesion contributed to a decline in MMSE, which suggests that parahippocampal or splenial involvement with an occipital lesion is associated with the cognitive decline seen after PCA infarction.

An unusual parahippocampal lesion presenting with seizures

A 27-year-old Caucasian man with a significant history of Dandy-Walker malformation with a ventriculoperitoneal shunt inserted in infancy and possible viral encephalitis at 3 years of age presented with classical complex, partial seizures from 12 years of age. Clinical examination did not reveal any focal neurological deficit.

An unusual parahippocampal lesion presenting with seizures

An unusual parahippocampal lesion presenting with seizures

Discrimination of social odors and their locations: role of lateral entorhinal area

Discrimination of individual conspecifics by their odors has been reported for many mammalian species, but little information is available on the brain mechanisms underlying such discrimination. A previous study reported that large parahippocampal lesions, centered on entorhinal cortex but extending into adjacent areas of the brain, eliminated female hamsters' ability to discriminate the flank gland odors of different individuals, as tested with habituation–dishabituation methods. The current study examined the effects of lesions restricted to the lateral entorhinal area on such discriminations. Female hamsters were tested in several types of habituation procedure that differed across a sequence of trials in the locations of familiar and novel social odors. Discrimination of two individuals' odors depended on the sequences of locations of the odors, indicating that odor identity and location were simultaneously salient to female hamsters. Lesions of lateral entorhinal area interfered with this spatial–olfactory discrimination. When confounding spatial cues were eliminated, hamsters did discriminate between novel and familiar odors, and lesions in the entorhinal area did not eliminate this ability. Thus, although the lateral entorhinal area is not necessary for individual odor discrimination, it is involved in processing odor–place combinations.

Corticohippocampal contributions to spatial and contextual learning.

Spatial and contextual learning are considered to be dependent on the hippocampus, but the extent to which other structures in the medial temporal lobe memory system support these functions is not well understood. This study examined the effects of individual and combined lesions of the perirhinal, postrhinal, and entorhinal cortices on spatial and contextual learning. Lesioned subjects were consistently impaired on measures of contextual fear learning and consistently unimpaired on spatial learning in the Morris water maze. Neurotoxic lesions of perirhinal or postrhinal cortex that were previously shown to impair contextual fear conditioning (Bucci et al., 2000) or contextual discrimination (Bucci et al., 2002) caused little or no impairment in place learning and incidental learning in the water maze. Combined lesions of perirhinal plus lateral entorhinal or postrhinal plus medial entorhinal cortices resulted in deficits in acquisition of contextual discrimination but had no effect on place learning in the water maze. Finally, a parahippocampal lesion comprising combined neurotoxic damage to perirhinal, postrhinal, and entorhinal cortices resulted in profound impairment in acquisition of a standard passive avoidance task but failed to impair place learning. In the same experiment, rats with hippocampal lesions were impaired in spatial navigation. These results indicate that tasks requiring the association between context and an aversive stimulus depend on corticohippocampal circuitry, whereas place learning in the water maze can be accomplished without the full complement of highly processed information from the cortical regions surrounding the hippocampus. The evidence that different brain systems underlie spatial navigation and contextual learning has implications for research on memory when parahippocampal regions are involved.

Paired-associate learning is unaffected by combined hippocampal and parahippocampal lesions in homing pigeons.

To examine whether the avian hippocampus-parahippocampus (HF) is necessary for nonspatial, paired-associate learning, as has been suggested for rodents, HF-lesioned and control homing pigeons were tested on a visual paired-associate learning task. Both groups learned equally well to discriminate trials that consisted of a stimulus preceded by its paired associate from trials that consisted of a stimulus preceded by stimuli from other paired associates (mispair trials), even when a mispair was experienced for the first time. The groups also learned equally well not to respond to 2 stimuli that were never rewarded. The results demonstrate that HF lesions do not impair nonspatial paired-associate learning in birds, suggesting that the role of HF in nonspatial cognition differs between birds and mammals.

Paired-associate learning is unaffected by combined hippocampal and parahippocampal lesions in homing pigeons.

To examine whether the avian hippocampus-parahippocampus (HF) is necessary for nonspatial, paired-associate learning, as has been suggested for rodents, HF-lesioned and control homing pigeons were tested on a visual paired-associate learning task. Both groups learned equally well to discriminate trials that consisted of a stimulus preceded by its paired associate from trials that consisted of a stimulus preceded by stimuli from other paired associates (mispair trials), even when a mispair was experienced for the first time. The groups also learned equally well not to respond to 2 stimuli that were never rewarded. The results demonstrate that HF lesions do not impair nonspatial paired-associate learning in birds, suggesting that the role of HF in nonspatial cognition differs between birds and mammals.

Sequential processing of “items” and “relations”

AbstractEichenbaum et al. (1994a) hypothesized that perceptually distinct items and the relations among them are processed sequentially by the parahippocampal region and the hippocampal formation, respectively. Predictions based solely on their model's sequential-processing feature might prove easier to disconfirm than those based on its representational features. Two such predictions are discussed: (1) double dissociations should be impossible following hippocampal vs. parahippocampal lesions, and (2) hippocampal lesions should not exacerbate impairments that follow complete parahippocampal lesions.

Learning and retention of a visual discrimination task in rats with various combinations of lesions in the temporal-hippocampal region

The temporal-hippocampal region appears to be critically involved in cognitive functions. Hippocampal or para-hippocampal lesions have been reported to impair learning and memory. Radical hippocampal lesions may, however, encroach upon the neighboring parahippocampal cortex, and the effects obtained are often attributed to hippocampal dysfunction alone. The present study was undertaken to examine whether damage to neighboring structures along with the hippocampus might have additive disruptive effects on learning and memory. Rats received either selective hippocampal (hippocampus proper, fascia dentata, subiculum) lesions alone or hippocampal lesions (Hipp) combined with damage to the temporal cortex (TC), the lateral entorhinal cortex (LEC), or the fiber connections between TC and LEC. Hipp lesions alone resulted in only impairment of the acquisition of a visual discrimination task, whereas Hipp + LEC lesions and Hipp + TC/LEC lesions produced marked deficits in both acquiring and retaining the same task. Hipp + TC lesions caused a milder impairment of both acquisition and retention. These results suggest that profound effects on learning and memory can be obtained when hippocampal lesions are combined with parahippocampal lesions.

Role of the parahippocampal region in spatial and non-spatial memory: Effects of parahippocampal lesions on rewarded alternation and concurrent object discrimination learning in the rat

Rats with aspiration or excitotoxic (NMDA) lesions of the parahippocampal region were trained on a series of behavioral tasks which consisted of: (1) a test of spatial memory (discrete trial rewarded alternation), (2) a black-white discrimination, and (3) a test of non-spatial memory commonly used in primate models of amnesia (visual concurrent object discrimination). Rats in both lesion groups were severely impaired on the concurrent discrimination, even though they were able to learn the black-white discrimination normally. Animals with aspiration lesions were also impaired on the spatial memory task, whereas those with NMDA lesions did not differ from controls. The results indicate that concurrent object discrimination is a particularly sensitive measure of hippocampal/parahippocampal functions and suggest that these structures in the rat may serve mnemonic functions which are qualitatively similar to those of human and non-human primates.