Clinical case report: memory functions after anterior communicating artery aneurysm rupture.

The case of a patient suffering from rupture of an aneurysm of the anterior communicating artery is reported. The hematoma was located in the basal forebrain, one of the anatomical regions associated with mnestic functions. Memory and other cognitive functions were studied. The patient performed well on all non-mnestic tests, but showed significant memory impairment. Anterograde memory was deficient not only in recall, but also in recognition. Performance on remote memory tests showed some differentiation. The patient remembered autobiographical material and famous faces correctly, but presented deficits on a Famous Events Test. This dissociation represents a difference in emotional content or familiarity of the material; the performance in tests using material with a higher emotional content was unremarkable. Lesions within the basal forebrain seem to deteriorate anterograde and remote memory, but performance may be inconspicuous if test material of high emotional content or familiarity is used.

Impaired declarative memory for emotional material following bilateral amygdala damage in humans.

Everyday experience suggests that highly emotional events are often the most memorable, an observation supported by psychological and pharmacological studies in humans. Although studies in animals have shown that nondeclarative emotional memory (behaviors associated with emotional situations) may be impaired by lesions of the amygdala, little is known about the neural underpinnings of emotional memory in humans, especially in regard to declarative memory (memory for facts that can be assessed verbally). We investigated the declarative memory of two rare patients with selective bilateral amygdala damage. Both subjects showed impairments in long-term declarative memory for emotionally arousing material. The data support the hypothesis that the human amygdala normally enhances acquisition of declarative knowledge regarding emotionally arousing stimuli.

Synaptic potentiation and depression in slices of mediorostral neostriatum-hyperstriatum complex, an auditory imprinting-relevant area in chick forebrain.

Long-term potentiation, a tetanic stimulation-evoked, persistent increase in synaptic efficiency, is the most extensively studied form of synaptic plasticity. Intracellular correlates of long-term potentiation have been analysed in mammalian hippocampus and cortex, but not in bird cortical analogues. We present here studies on long-term potentiation in slices of the chick forebrain area mediorostral neostriatum-hyperstriatum complex which receives thalamic afferents and is relevant for auditory filial imprinting. Following afferent tetanic stimulation, population spike potentiation was extracellularly recorded in 25% of the tested neurons for longer than 40 min. Using intracellular recordings, the membrane potential, the amplitude of excitatory postsynaptic potentials, the latency between the test stimulus and the evoked action potentials, and the cellular excitability (excitatory postsynaptic potential-spike relationship) were found to change after the tetanus. A long-term depression following the tetanus was also seen in some units in this area. Furthermore, the mechanisms underlying long-term potentiation were investigated. A large depolarization of resting membrane potential (approx. 36 mV) was characteristic after the tetanic stimulation. N-methyl-D-aspartate receptor channels are necessary for induction of this depolarization, as well as for long-term potentiation, as demonstrated by the effect of DL-2-amino-5-phosphonovaleric acid. After intracellular recordings, the cells were injected with Lucifer Yellow. The combination of electrophysiological characterization and morphological identification suggested that the potentiation came chiefly from type I neurons, which have the largest soma among the neuron types in this area and up to eight dendrites. The results demonstrate that the recognized major phenomena of long-term potentiation are found in an auditory imprinting-relevant area of the chick forebrain, and that this potentiation is dependent on N-methyl-D-aspartate receptor channels. It is noteworthy that behavioural imprinting was previously shown to induce a reduction of up to 47% of the spine frequency of type I neurons and a growth of the remaining spine synapses, all resembling a synaptic selection process. Therefore, the intriguing possibility emerges that mechanisms underlying long-term potentiation are instrumental for this selection process, which involves regressive and proliferative morphological changes.

The amygdala's contribution to memory--a study on two patients with Urbach-Wiethe disease.

The consequences of primary amygdaloid damage on memory performance are described in terms of neuropsychological, CT, MRI and PET results of two patients, a brother and a sister. Both had circumscribed, bilaterally symmetrical damage confined to the amygdaloid region, while the hippocampal formation and other brain structures were intact. PET-imaging furthermore revealed an overall decrease in glucose metabolism which was particularly apparent at the cingular and thalamic levels. Although neither patient was amnesic, both showed memory impairments in selective tests. In one patient these impairments were more pronounced and they were accompanied by marked affective-emotional fluctuations. Our results suggest that the amygdaloid region is a bottle-neck structure that confers an affective flavour to memories, thereby enhancing the probability of their long term storage.

[The structure of mnestic problems in multiple sclerosis: everyday memory performance and neuroradiologic findings]. / Zur Struktur mnestischer Probleme bei Multipler Sklerose--Alltagsgedächtnisleistungen und neuroradiologische Befunde.

35 multiple sclerosis patients and 30 matched healthy controls were investigated for mnestic problems using a German everyday memory test. The objects were both the description of structural characteristics of disturbances and "ecological validity" to meet rehabilitative issues prospectively. In the MS group, impairments were found mainly in the memory domain under delayed recall conditions of complex material. The processing of these tasks may be especially sensitive against fiber tract lesions. While discrete lesions, mostly found in patients with relapsing-remitting courses, inconsistently lead to partial memory disturbances, global mnestic deficits are to be expected in confluent lesion patterns exceeding a critical "threshold of cerebral tolerance." The latter characterises mostly patients with chronic progressive disease courses.

Everyday memory impairment, neuroradiological findings and physical disability in multiple sclerosis.

Thirty-five multiple sclerosis (MS) patients diagnosed according to the Poser criteria were examined in a variety of cognition and memory tasks. Their performance was compared to age- and gender-matched healthy individuals. While there was no difference in overall intellectual performance and short-term memory between the MS group and control subjects, the patient group showed significant deficits in several everyday memory tasks including story recall, object and face recognition, procedural, topographical and prospective memory tasks. An intra-group comparison in the MS cohort revealed that those patients with a chronic-progressive MS course exhibited the most substantial everyday memory impairments and highest EDSS scores. These findings coincide with the neuroradiological, semiquantitative lesion analysis which was also performed. In this analysis, the latter MS subgroup also had the highest lesion score, as a sign of an overall brain involvement.

The possible contribution of the amygdala to memory.

The processing of episodic memories is believed to depend on the proper functioning of so-called bottleneck structures through which information apparently must pass in order to be stored long term. These regions are seen in the basal forebrain, the medial diencephalon, and the medial temporal lobe. We here report a case with circumscribed bilateral temporal lobe damage, principally involving the amygdaloid area. Neuropsychological investigation demonstrated preserved intelligence, intact general memory and several other undisturbed cognitive functions, but a specific, affect-related, memory disorder. We conclude from these findings that the role of the amygdala is to process mnemonic events in a way that a specific emotional significance can be found and reactivated. Therefore it is suggested that the amygdala is likely to be a bottleneck structure for affect-related long-term memory functions.