Another article in Science News (4/30/16) shows our further understanding of this remarkable structure and lets me speculate even more. This new report is about research that shows that the hippocampus maps social objects, i.e., conspecifics or people if you are Homo sapiens as in the experimental study, or maybe rats if you are a rat, a mammal in which the hippocampus evolved early to serve memory especially for spaces and sounds in their case. This brings up two issues: one is how we conceptualize and talk about such phenomena and our research into them and the second is the difference between experimental laboratory studies and in vivo ecological studies, i.e., real life not the lab, and my speculation on what we will find we can do more of the latter.
To review a bit for the newer readers of my blog, the hippocampus (actually hippocampi, right and left) is a cortical structure which receives input of highly processed information from the posterior perceptual areas for processing as old or new, remembered or to be remembered, and feeds its results into frontal areas to support intentional guidance. It is one of my favorite areas for discussion so I have several blog posts on it over the years. It is an area between midbrain and cortex, so that is either at the peak of midbrain evolution and operates as the cortex for the limbic system, the emotional core of the brain or at the beginning of the neocortex and the evolution of the cerebral hemispheres and higher cognition.
Hippocampus on the left side under the cut away cortex and on top of the limbic system
The Science News article focuses on studies with rats when mapping tonal sequences or time’s passage is important and a study with humans undergoing a computer simulation of hunting for a new home or job. The subjects interacted virtually with different characters and formed judgments about their power and approval of the subject. The interaction with the virtual characters correlated with activity in the hippocampus and upon further analysis, the judgments formed correlated with some behavioral traits associated with social anxiety. So imagine in the real world, going to a party with mostly familiars or with mostly strangers, we would imagine that our hippocampi would keep up with, i.e., map, the people we meet in different ways for strangers and familiars, that people with different social approaches, e.g., low or high social anxiety, introversion or extroversion, would map the interactions quite differently and subsequently remember the events quite differently. So later on, say that night while sleeping, the hippocampi would consolidate particular memories of the party; they would extract the more salient experiences for memory input based upon their emotional stance.
The articles I read in Plosbiology are quite technical and I can only partially digest them. Still what I can glean there is interesting. They all used the electrical activity (EEGs of various sorts) to correlate with behavioral/mental activity. One looked at how the hippocampus grows quieter during REM (dream) sleep, where by quieter I mean more synchronized, i.e., less analysis going on, and with lower energies. This would seem to indicate that its role as memory organizer for input has momentarily paused while the selected memories are consolidated for later recall. Another article reports research showing that, contrary to current thinking and models, memory input-recall is done unconsciously as well as consciously. Many currently think conscious processing is needed for input and recall, though why I do not know. There is a lot of literature now showing that subconscious processes do much of the work—see Malcolm Gladwell’s book Blink for one perspective on this.
The third article is the most interesting to me because it shows differences between right and left hemispheres in detecting new information. Specifically the left hippocampus works more at detecting violations of expectations while the right hippocampal circuit monitors novelty and changes more generally. Are we using our left sided linguistic abilities to set and codify expectations for monitoring? Sure, look at the science about inner speech. Is the right side more concerned with the ongoing present, our consciousness being the remembered present (to use William James’ term)? Sure, look through my blog.
Now all these studies looked at the brain’s and the hippocampus’ response to events impacting our perceptual systems as set up by experimental designs. Leaving the strictly positivistic behind while still remaining empirically oriented I want to ask about functioning in the natural world (in vivo and ecological), about how we talk about hippocampal processing, and most especially, about the brain’s own creative processes that underlie artistic activity.
Consider how the hippocampus and its functions presumably develop early in life. Mostly immature at birth it quickly matures during the sensitive early years to acquire the ability to map space and time, things, and animate objects, not just people–remember toddlers’ affinities to other animals, especially dogs. These social maps, in conjunction with other areas such as the higher visual cortex for facial recognition and the lower limbic areas for attachment and emotional regulation, come to demarcate family and intimates from others, familiars from strangers and safety from danger. Imagine the impact on these incipient maps when intimates turn out to be dangerous as happens in instances of childhood maltreatment. Treasure the impact of healthy families on these same maps.
Consider what is actually being mapped here. Yes, experimental science, in order to progress in a sure-footed manner, must study aspects with careful controls. So studies have shown that the hippocampus maps space, time, things, and others. In a more holistic sense the hippocampus maps our experiences. Remember the patient H.M. (see post on ) who had a bilateral hippocampectomy, i.e., surgical removal of both hippocampi, in the effort to control severe epilepsy. He lost the ability to make new memories even though he could remember educational material and some events from his long past. He failed to recognize his doctors and other medical personal and the scientists studying his neuropsychological deficits even though he saw some of them almost every day, even though he had seen them an hour beforehand. He could converse and express himself on many topics and retained some procedural memories of how to do things. One conversation I find remarkable is reported in Joseph’s Neuroscience text. H.M. asked someone what he had done in the past little while because he was worried he may have done something wrong. He knew he had done something but he did not know what and so worried about that. His consciousness lacked the experience of the remembered present. (To my mind his worries mark him as a true gentleman as opposed to some politicians and sociopaths who worry about this not at all).
Consider what we do not know about hippocampal functioning during artistic endeavors such as dance, novels or music. I am quite sure that dancing, at least well with others, involves hippocampal maps for guidance. Ritualized and choreographed motions would necessarily involve maps for space, time, and others as well as procedural memories for the actual movements. Ritualized motion would summon emotional involvement in a consistent acculturated manner; modern choreographed motions would summon emotional involvement in a dramatic manner. What about novels with their virtual space, time, characters and experiences, all from different perspectives? Here I do not think we know much about how the hippocampus might function in support of the virtual domains involved and I do not think the hippocampus as a part of the perceptual-motor system dealing with objective events is sufficient for virtual operations. For these I think that dorsal and ventral loops involving longitudinal fasciculi in the cortex must contribute (see post Important stuff 2/11/16). So I wonder how Faulkner knew Yoknapatawpha County so well and how Gandalf and Aragorn knew all the paths of Middle Earth.
Finally consider music that I have focused on here so recently. Memory for tones, rhythms, melodies, beats seem basic and probably involve procedural memories as well. Memories for the biographical frames of favored songs are among the last to be lost with dementia, sometimes lasting even after one’s own identity is forgotten. This highlights again an important feature of hippocampal functioning, the setting of a standard or the stabilizing memory of the song’s emotional tone and echoes in a fashion analogous to its noticing things are out of place or out of order as reported in the previously cited studies and in H.M.’s worries. We experience only as we are able to fit moments together and this requires that we organize our mental functions coherently in an integrated fashion as moments in our life. Somehow our brains know what melodies work for a particular culture–no atonal tunes for me please–and some brains know innovative genius upon hearing; think of the responses to Stravinsky’s Rite of Spring. So good job, hippocampus, and thanks for the memories.