Removal of the Hippocampus

Aggleton, J. P., Keith, A. B, Rawlins, J. N., Hunt. P. R, and Sahgal. A. (1992). Removal of the hippocampus and transection of the fornix produce comparable deficils on delayed non-matching to position by rats. Behav. Brnin Res. 52, 61-71. 

In explaining the function of the hippocampus—the brain structure in the medial temporal lobe of our brains—she says, That is what is active right now as you are trying to learn what I am telling you. Removal of the hippocampus leads to profound amnesia, and it is an amnesia where you cannot learn new information. She offers the example of Tom Hanks as Mr. Short-Term Memory on the old Saturday Night Live episodes. He walks out the door and crows, Nice to meet you completely unaware that they had met moments earlier. 

Figure 8.1 Diagram of hippocampus dissection procedure. (A) Removal of the brain from the embryo. From left to right (1) The embryo is grasped with a pair of large straight forceps the brain under the skull is visible. (2) Make the first cut at the brain...

Amnesia patients showed the role of temporal lobe in memory. Almost at the same time of Penfield s studies, Brenda Milner of the Montreal Neurological Institute examined a patient, known by his initials as H. M., who had undergone bilateral surgical removal of the temporal lobe (medial temporal cortex, amygdala, and two-thirds of the hippocampus). The surgery was apparently a success... 

The mu, delta and kappa opioid receptors are coupled to G° and G proteins and the inhibitory actions of the opioids occur from the closing of calcium channels (in the case of the K receptor) and the opening of potassium channels (for /i, d and ORL-1). These actions result in either reductions in transmitter release or depression of neuronal excitability depending on the pre- or postsynaptic location of the receptors. Excitatory effects can also occur via indirect mechanisms such as disinhibition, which have been reported in the substantia gelatinosa and the hippocampus. Flere, the activation of opioid receptors on GABA neurons results in removal of GABA-mediated inhibition and so leads to facilitation. 

That the hippocampus is important for memory is generally accepted. This is not because it is a site of major degeneration in AzD, that finding can only be used to account for the memory loss if memory is known to be dependent on the hippocampus, but because lesions of that region are known to impair memory. Case reports in the medical literature are rightly mistrusted but few people have felt inclined to disregard the evidence presented by one 27-year-old male mechanic who underwent bilateral hippocampal removal for intractable epilepsy in Montreal in 1953. While that condition was improved the operation has not been repeated because memory loss was almost total, so while he appeared to behave reasonably normally (and still does), he cannot remember where he lives, what he has just eaten or the person he met a few minutes previously. 

The proposed neurogenesis-memory clearance hypothesis is attractive because addition and removal of adult-born neurons in local network architecture could gradually destabilize the stored memory traces. Also, adult-generated neurons within the dentate gyrus, the upstream location in the hippocampus, potentially can amplify the destabilization effects. Coincidently, these newborn neurons are short-lived, typically with a life-span of three weeks in rodents [40], which seems to correlate well with the duration of hippocampal dependence of declarative memories. 

Ginkgo alters lipid metabolism created by electroconvulsive shock treatments. EGb 761 reduced accumulation of free fatty acids and removal of diacylglycerol, which is more pronounced in the hippocampus than cerebral cortex (Rodriguez de Turco et al. 1993). Ginkgo also has protective effects on lipid membranes under hypoxic conditions. Bilobalide, but not ginkgolides, suppressed hydrolysis of choline induced... 

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