More important than divide memory in short-term or long-term is classify them in episodic or semantic. According to Multiple Trace Theory, long-term episodic memories are stored in hippocampus, so mild AD patients, even MCI, will lose these kind of "long-term" memories. Long term semantic memories will be lost in parallel with neocortex neuron death.

Yes good point, but in late stage disease, there are almost no memories or even the abilty to recognize those people very close to you  - or so it seems

There is strong evidence that memories take time to become independent. For example HM could remember events from his childhood but not for the years preceding his surgery. Alzheimer's isn't just a disease of the hippocampus. Although pathology starts in the MTL it expands outward into the neocortex. There are wide scale disruptions of metabolism, synaptic dysfunction, cellular death, and atrophy. You also need to dissociate storage and retrieval mechanisms. A memory could be stored independently of the hippocampus, but may require the hippocampus or other MTL structures to properly be retrieved.

Brian, you should check out: http://www.ncbi.nlm.nih.gov/pubmed/15716139 for a more recent interpretation of H.M.'s autobiographical memory impairment. This work suggests that he actually had highly impoverished event memories, both recent and remote, in accordance with theoretical frameworks that argue that the hippocampus is involved in remembering events no matter how remote. :)

The basic disorders by so called "AD"  are the speech disorders - sensoric aphasio (Anomio) and than the secondary pseudo or real memory deficits. Similar to Dementio paralitytia (Neurosyphilis).

Just adding to Daniela and Guilherme's comments, when semantic and episodic LTM are assessed in patients with amnesia there is a relative spare of semantic memories despite the episodic deficit, and that was the case in HM as the paper cited by Daniela demonstrates. A similar dissociation appears in AD, particularly at the beginning. I understand that old memories or  family members may indeed be affected at later stages, but I guess that the progress of neural degradation through the cortex must contribute to it.

I agree with Dr. Gordon.  The disease process begins in association areas of cortex and in the dentate gyrus of the hippocampi, for as yet unknown reasons.  Eventually it involves the entire cortex as well as subcortical structures.  As apoptosis occurs, there is less connection throughout the brain leading to gross atrophy.  Cell death involves vascular changes as well as inflammatory processes impinge on capillaries.  Long term memories appear to be diffusely stored, but with enough cortical and subcortical breakdown, they cannot be accessed.

Benedict,

My hypothesis, which I am discussing on some other threads here on RG at present, could possibly explain (at least some) of your findings. The bad news: my hypothesis is far away from being accepted in the scientific community. (Anyway, I confess that my attempt is a scientific one without any restriction! No esoterism!) A famous German neuroscientist wrote me, if I would be right, his (alike) famous colleague X and his coworkers would have recognized this before. Now you are prewarned!

You may have a look on my Essay which is “published” on RG only! If you like it and you or somebody else of the audience is interested to discuss with me, just give me a feedback!

http://dx.doi.org/10.13140/2.1.1087.2009

Brief introduction:

(1) For me, all and any “information” that reaches the brain from the outside world is made up by waves and oscillations, and it will be processed within the brain in form of waves and oscillation. Waves and oscillations – as far as they are coherent – can be recorded and chronicled as holograms. And they can be reconstructed – recalled – by the same type of waves and oscillation that have built the holograms. If parts of the holograms or parts of the endogenous waves and oscillations are destroyed, multiple deficits become noticeable. There is much different possible causation. It just depends!

(2) Memory is distributed all over the brain. Not homogenously, but with special foci. Special brain areas and special neurotransmitters, modulators and hormones are responsible for special waves and oscillations. They all can show deficits that affect the whole.

(3) This holds for any kind of memory. Independent if it is short-term or long-term, episodic or semantic, even sensory-motoric. Often, but not always, the hippocampus is required. It depends.

(4) For me, the hippocampus seems to be absolutely indispensable for the transformation of short-term to long-term memory. For many other tasks and processes it might not be essential.

Ursula

A Culture–Brain Link: Negative Age Stereotypes Predict Alzheimer’s Disease Biomarkers.Levy, Becca R.; Ferrucci, Luigi; Zonderman, Alan B.; Slade, Martin D.; Troncoso, Juan; Resnick, Susan M.

Psychology and Aging, Dec 7 , 2015, No Pagination Specified. http://dx.doi.org/10.1037/pag0000062

Abstract

Although negative age stereotypes have been found to predict adverse outcomes among older individuals, it was unknown whether the influence of stereotypes extends to brain changes associated with Alzheimer’s disease. To consider this possibility, we drew on dementia-free participants, in the Baltimore Longitudinal Study of Aging, whose age stereotypes were assessed decades before yearly magnetic resonance images and brain autopsies were performed. Those holding more-negative age stereotypes earlier in life had significantly steeper hippocampal-volume loss and significantly greater accumulation of neurofibrillary tangles and amyloid plaques, adjusting for relevant covariates. These findings suggest a new pathway to identifying mechanisms and potential interventions related to the pathology of Alzheimer’s disease. (PsycINFO Database Record (c) 2015 APA, all rights reserved)

Alzheimer's pathology appears very early in the hippocampus and entorhinal cortex. In the advanced stages of the disease, it is also neocortically distributed in a way that disturbs stable and long-lasting memories - that's the answer to your question.