Platelet aggregation in transient global amnesia

Platelets and psychiatry: lessons learned from old and new studies

Platelets play an important role not only in hemostasis but also in the pathophysiology of coronary artery disease. The complex interactions among the vascular endothelium, platelets, and blood components are one of the most exciting research areas today. This review addresses some fundamentals of platelet physiology and examines why platelets are interesting probes for neurophysiology. Results of current studies suggest that platelets are affected by diverse stressors, including psychological ones, and that platelets offer an interesting vantage point for understanding the neurophysiology of various psychiatric disorders. We also describe how platelets have been used for various types of research, including studies of stress associated with cardiovascular disease and studies of platelets in psychopharmacological research. Finally, we examine some of the psychiatric literature related to platelets; these studies range from case studies from the 1920s to contemporary experimental studies.

Transient global amnesia

Transient global amnesia (TGA) is a transient, benign neurological syndrome, characterized by global loss of memory, preserved consciousness and self-awareness, associated with some behavioral changes (in particular, repetitive questioning). It generally resolves within 24 h. Mild brain stem symptoms can often be demonstrated during the attack, but major neurological abnormalities never occur. The only sequel is a permanent amnesic gap for the duration of the episode. The episode is often preceded by typical precipitating events, such as physical activity, emotional stress, acute pain, comprising haemodynamic changes of the body. The diagnosis is easy provided one is acquainted with the syndrome. The prevalence of vascular risk factors is low and the risk for stroke is not increased. Although much evidence indicates the possibility of a causative ischaemia in the inferomedial parts of the temporal lobes, an atherothrombo-embolic TIA is not the cause of TGA, and TGA is unrelated to cerebrovascular disease in general. In the author's view, the cause of TGA is a transient ischemic attack (TIA) but a haemodynamic one of the vertebrobasilar system, producing a transient dysfunction of inferomedial parts of the temporal lobes, regions that are particularly sensitive to impaired blood supply. For a full pathogenetic explanation of TGA, clarification of the underlying mechanisms is a prerequisite. This touches on the genesis of migraine and Leao's spreading depression phenomenon. The term 'amnesic TIA' would reflect the pathogenesis more appropriately.

Transient global amnesia after cerebral angiography with iohexol

We describe a patient without a previous history of migraine or epilepsy and with no known vascular risk factors, who suffered subarachnoid haemorrhage. During vertebral angiography using nonionic contrast medium (iohexol), spasm of the basilar artery was seen. The patient suffered transient global amnesia. Angiography 3 months later with the same contrast medium was normal and produced no further deficit. This case lends support to the supposed ischaemic aetiology of transient global amnesia; in patients without other evidence of cerebrovascular disease, arterial spasm may be responsible.

Memory loss due to transient hypoperfusion in the medial temporal lobes including hippocampus

A typical case of transient global amnesia (TGA) was investigated with single photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI) with 1.5-tesler scans. During the amnesic episode, a marked decrease of cerebral blood flow was observed in the areas confined to the territory of the bilateral posterior cerebral arteries including the hippocampus. After the episode, cerebral blood flow returned to normal and a circumscribed lesion was detected in the middle portion of CA 1 field of the left hippocampus. The SPECT findings prove direct evidence that the medial temporal structures are involved in the establishment of new memories, as well as in process of recalling only recently acquired memories, but not in retrieval of memories acquired long ago. The MRI findings indicate that a unilateral partial damage to CA 1 sector of the hippocampus does not develop a definite memory impairment and that high-resolution MRI study on the hippocampus is necessary in TGA patients.