A new San Diego study finds that patients who can't remember what they did just moments before can still find their way around using a map. The researchers say this finding comes as a surprise, because the patients involved in the study had damage in a part of the brain thought to play an important role in spatial navigation.
"There's been a long tradition of uncertainty about the function of a particular part of the brain called the hippocampus," said lead researcher Larry Squire, a UC San Diego neuroscience professor and scientist with the Veterans Affairs Medical Center, San Diego.
The hippocampus has long been known to be crucial for long-term memory formation. Squire and his colleagues wanted to know if it also plays an important function in spatial navigation, as some previous research has suggested. One intensely studied patient with profound hippocampal damage, Henry Molaison, reportedly had trouble using a map, though experts say details on that are sketchy.
The researchers designed some experiments. They used floor markings to lay out paths in their lab. They had patients navigate their way through these paths using a map they could keep handy throughout the experiment. Some of these patients had typical, functioning brains — others had hippocampal damage that left them memory-impaired.
In a study published Monday in PNAS, the researchers found that the five patients with hippocampal damage were able to use a map just as well as people without such damage.
"The patients were forgetful of what they'd just been doing as they performed the task, but we found that they were entirely intact at navigating the path shown on the map," Squire said. "What we've learned is that the ability to navigate is separate from the ability to form new memories."
One patient offered clues about where the brain's navigation center may be located. This patient's damage was not limited to the hippocampus — it appeared to also affect the surrounding parahippocampal cortex. Unlike the others, this patient failed to match the control group in map-reading ability.
"It's a little difficult to know how to interpret this. It's just one patient," Squire said. "More work's going to be needed to understand why this single patient had difficulty."
Institute for Brain and Society director Jacopo Annese, a neuroscientist who was not involved in the study, told KPBS via email that he liked how the study "challenges classic views of hippocampal function."
But he said it's hard to tell the extent of the hippocampal damage in some of the patients who participated in this study. Two have had their brains examined up-close in autopsies, but Annese said without a detailed look at the other patients' brains, "It is difficult to generalize the results."
Squire said this study is part of a larger attempt to understand how the brain creates memory, so that memory impairments might one day be treatable.
