Neuropsychologists and scientists are still not in total agreement over whether forgetting is due to faulty encoding, accelerated forgetting, or faulty retrieval, although a great deal of data seem to point to the encoding hypothesis. In addition, neuroscientists are also in disagreement about the length of time involved in memory consolidation. Though most researchers, including Hasselmo et al., have found the consolidation process is spread out over several hours before transitioning from a fragile to a more permanent state, others, including Brown et al., posit that memory consolidation can take months or even years in a drawn-out process of consolidation and reinforcement. Further research into the length of time of memory consolidation will shed more light on why anterograde amnesia sometimes affects some memories gained after the event(s) that caused the amnesia, but does not affect other such memories. Medial temporal lobe
The MTL memory system includes the hippocampal formation (CA fields, dentate gyrus, subicular complex), perirhinal, entorhinal, and parahippocampal cortices. It is known to be important for the storage and processing of declarative memory, which allows for factual recall. It is also known to communicate with the neocortex in the establishment and maintenance of long-term memories, although its known functions are independent of long-term memory. Nondeclarative memory, on the other hand, which allows for the performance of different skills and habits, is not part of the MTL memory system.
Echocardiography is also used if there is a suspicion of pulmonary hypertension or high-output cardiac failure due to large liver lesions, sometimes followed by cardiac catheterization to measure the pressures inside the various chambers of the heart. Liver AVMs may be suspected because of abnormal liver function tests in the blood, because the symptoms of heart failure develop, or because of jaundice or other symptoms of liver dysfunction. The most reliable initial screening test is Doppler ultrasonography of the liver; this has a very high sensitivity for identifying vascular lesions in the liver. If necessary, contrast-enhanced CT may be used to further characterize AVMs. It is extremely common to find incidental nodules on liver scans, most commonly due to focal nodular hyperplasia (FNH), as these are a hundredfold times more common in HHT compared to the general population. FNH is regarded as harmless. Generally, tumor markers and additional imaging modalities are used to differentiate between FNH and malignant tumors of the liver. Liver biopsy is discouraged in people with HHT as the risk of hemorrhage from liver AVMs may be significant. Liver scans may be useful if someone is suspected of HHT, but does not meet the criteria (see below) unless liver lesions can be demonstrated.Brain AVMs may be detected on computed tomography angiography (CTA or CT angio) or magnetic resonance angiography (MRA); CTA is better in showing the vessels themselves, and MRA provides more detail about the relationship between an AVM and surrounding brain tissue. In general, MRI is recommended.