What is pattern separation?
Pattern separation is the brain's way of detecting novelty by noticing subtle distinctions in the scene around us. Today most of us live and work in the built environment and don't need to keep a finely trained eye out for subtlies in our surroundings to find food and survive. Yet scientists indicate that our brains may still be wired for exploring regularly like humans did for nearly 2 million years. This implies that our pattern separation circuity is under-utilized today.
Decreased use of pattern separation (aka novelty detection) in scenes may be a critical piece of the puzzle regarding atrophy in the brain's hippocampus according to a paper by Lindy Birkel that was recently published in Medical Hypotheses: doi.org/10.1016/j.mehy.2017.07.012 . Atrophy - or reduced volume - of the hippocampus is associated with conditions from chronic stress to at least 20 neuropsychiatric disorders including depression, anxiety and Alzheimer's disease. On the positive side, employing the hippocampus in pattern separation to detect subtle changes in scene may boost the hippocampus and improve these aspects of mental health.
Where can I find out what my hippocampal volume is?
Right now, there are limited options for getting a structural MRI (Magnetic Resonance Image) to determine the volume of your hippocampus. You may consult your physician for a prescription. In addition there are efforts to refine clinical protocols such as the Alzheimer’s Disease Neuroimaging Initiative (ADNI), which performs a number of annual tests on research participants, including structural MRI. To qualify, participants need to be within the ages of 55-90 and satisfy a number of other requirements. For more info: adni.loni.usc.edu/.
In lieu of getting a scan, performance in pattern separation has proven to be a good indicator of hippocampal volume. The MST test, developed at UC Irvine and designed to test pattern separation, is utilized in research at several labs. Performance on the MST pattern separation test correlates well with hippocampal volume (1, 2), though the test is not currently provided through public venues.
What the MST test results do suggest, however, is that using it to practice and improve pattern separation performance may stimulate activity in the hippocampal region most strongly associated with atrophy. That is what we are focused on here. Our Pattern Separation Challenges are modeled after the UC Irvine MST test with the intention of stimulating pattern separation activity in the dentate gyrus/CA3 region of the hippocampus. Here, pattern separation activity is associated with BDNF secretion, which facilitates neuroplasticity and therefore growth of neuronal connections (3, 4). This makes pattern separation activity a likely vehicle for increasing hippocampal volume. We are also collecting (anonymous) data about performance on our Pattern Separation Challenges but are not, at this time, involved in scans of the hippocampus.
The future for regular access to structural MRI in the clinical setting is bright. It is plausible that at some time in the not too far distant future we’ll all get regular brain scans the way we, for example, have our blood pressure routinely checked today. With improvements in resolution, future scans may more easily identify regions of the brain that could use bolstering than they do today. Prescriptions for how to increase activity in those regions could then be provided. This is an entirely possible future for keeping the hippocampus and all of its associated mental health issues in shape. Stay tuned.
What novelties in scenes do we distinguish with the pattern separation circuitry?
Pattern separation happens where sensory information first enters the hippocampus in a region called the dentate gyrus. Here our impressions of the background scene are combined with objects, sounds, smells etc. to create a full impression of our surroundings (5, 6, 7).
We may detect that something, like a type of rock, indicates we're in a specific navigational location (8, 9). Similar locations that are close together may also appear to change their positions relative to one another as we move (10). We're also aware of background as, for example oak forest, very subtlely grades into a mixture with pines and then into a pine forest as elevation increases. These subtleties are likely noticed through pattern separation (11).
We'll also detect movement and as we move, we'll detect the changes in our view. Angular rotations of animal heads, legs, and/or wings underlie movement - and we can pick up on very subtle movements through these positions. Irregularities in these movements might also be detected, for example as a lion scans a herd to identify a less fit animal. Weakness may be revealed through slight differences in angular rotations of limbs compared to the rest of the herd. Tree branches may also make angular movements in a breeze or as animals move through them (12). We also quickly notice if an object, like an animal, changes its position relative to the background scene (13) OR objects, like animals or rock outcrops, will appear to change position relative to the background scenery, as we move and we'll note that through pattern separation as well. We'll also notice movement through changes in the positions of objects like animals relative to one another (14).
The shape of the environment we're in, whether it is defined by rocks, hills, open expanses or some combination of features, will also appear to change as we move and we'll likely track that kind of change through pattern separation (15). Recognizing locations when they appear different from alternate angles of approach is an important skill in navigation.
The perceived color of the environment - or shades of gray in shadows - change throughout the day and we can monitor that through pattern separation (16). Color may also provide other indications. For example, a herd of buffalo may kick up dust if they pass through a bare patch of land. Dust could create a change in the color of the sky along a patch of horizon, thus indicating where animals are.
We may also detect subtle changes in odor in a scene. This might help in detecting an animal or a plant prior to having it in our sights (17).
Beyond these studied parameters of scene that utilize pattern separation, there are likely more. For example, detecting an animal camouflaged within its surrounding context will likely require the fine-grained distinction capability of pattern separation, though this has not yet been studied.
Can you think of other examples? Let us know!
Do we use the pattern separation circuitry to detect novelty in the grocery store?
There are several reasons why it’s unlikely that we utilize pattern separation in the grocery store to an extent equal to our ancestral food acquisition-related use of pattern separation in the wild environment:
Data suggest that we spend only about an hour per week per household in the grocery store (18, 19) whereas, hunter-gatherers may spend a few days per week obtaining food (20). And while we work for paychecks in order to be able to buy food at a grocery store, the work we do rarely requires that we make fine-grained distinctions of our work environment.
Though shopping for food at a grocery store does involve a number of discriminations, it is unlikely that these utilize pattern separation. That's because branding strategies typically lead us to circumvent sensory discrimination in making our choices. Studies show that we're more likely to rely on the words used on labels, rather than the sensory qualities of the products themselves (21, 22).
Perhaps the recognizable marks of a branded label in a grocery store can be compared to the field marks used to identify animals. However brands are designed to catch shopper's attention, effectively shouting that they be selected for dinner. Meanwhile everything in nature employs strategies NOT to be selected for dinner (including field marks, which often provide camouflage).
Along these lines, consider also the signs and billboards that may advertise dinner at a restaurant. Signs and billboards are also attention-grabbing and typically don't require searching to find. Compare siting these to finding the track of an animal. On detecting a track, hunters don't proceed straight to the animal and pull out some cash. Hunters instead call up past experiences hunting that animal and compare those memories to the present situation. In doing so the hunter typically examines multiple aspects of the scene before deciding which way to turn. Through a gradual process of making further discriminations that likely require pattern separation, the hunter will attempt to spot the animal and may or may not succeed in capturing it.
These are several examples of how food acquistion today likely requires less pattern separation activity than that of hunter-gatherers. Perhaps you can think of other examples. Let us know!
Is hippocampal volume an inherited trait?
There is evidence suggesting that hippocampal volume is a heritable trait (23, 24).
With the sudden and sweeping shifts in environment and behavior from hunting and gathering to agriculture and then industrialization, reductions in hippocampal volume that are related to lack of use of pattern separation could have instigated epigenetic change in human DNA. Persistently low levels of pattern separation activity in today's lifestlyes could contribute to further declines in hippocampal volume and/or increase the number of people with lower volumes. Fortunately evidence supports the concept that increasing cognition and behaviors associated with atrophy, like pattern separation, could improve hippocampal volume and mental health. This sort of effort could also be a basis for positive epigenetic change.
What are the mental health disorders that are associated with hippocampal atrophy?
Hippocampal volume is found in chronic stress in otherwise healthy individuals and appears to further decrease along a continuum to those with diagnosis of mental health disorders (25).
In a literature review of studies that used MRI to determine hippocampal volume, the following conditions were found in association with lower hippocampal volume (26):
mild cognitive impairment
traumatic brain injury
Herpes simplex encephalitis
survivors of low birth weight
posttraumatic stress disorder (PTSD)
borderline personality disorder
antisocial personality disorder
1. Doxey CR, Kirwan CB. Structural and functional correlates of behavioral pattern separation in the hippocampus and medial temporal lobe. Hippocampus 2014;25(4):524–33.
2. Stark SM, Stark CEL. Age-related deficits in the mnemonic similarity task for objects and scenes. Behav Brain Res 2017;333:109–17.
3. Bekinschtein P, Kent BA, Oomen CA, et al. BDNF in the dentate gyrus is required for consolidation of ‘‘pattern-separated” memories. Cell Rep 2013;5:759–68.
4.Bekinschtein P, Kent BA, Oomen CA, et al. Brain-derived neurotrophic factor interacts with adult-born immature cells in the dentate gyrus during consolidation of overlapping memories. Hippocampus 2014;24:905–11.
5. Hargreaves Elm Rao G, Lee I, Knierim JJ. Major dissociation between medialand lateral entorhinal input to dorsal hippocampus. Science 2005;308:1792–4.
6.Hunsaker MR, Mooy GG, Swift JS, Kesner RP. Dissociations of the medial and lateral perforant path projections into dorsal DG, CA3 and CA1 for spatial and nonspatial (visual object) information processing. Behav Neurosci 2007;212 (4):742–50.
7. Morris AM, Weeden CS, Chruchwell JC, Kesner RP. The role of the dentate gyrus in the formation of contextual representations. Hippocampus 2013;23 (2):162–8.
8. Dees RL, Kesner RP. The role of the dorsal dentate gyrus in object and object-context recognition. Neurobiol Learn Mem 2013;106:112–7.
9. Spanswick SC, Sutherland RJ. Object/context-specific memory deficits associated with loss of hippocampal granule cells after adrenalectomy in rats. Learn Mem 2010;17(5):241–5.
10. Clelland CD, Choi M, Romberg C, et al. A functional role for adult hippocampal neurogenesis in spatial pattern separation. Science 2009;325:210–3.
11. Ahn J-R, Lee I. Intact CA3 in the hippocampus is only sufficient for contextual behavior based on well-learned and unaltered visual background. Hippocampus 2014;24(9):1081–93.
12. Neuneubel JP, Knierim JJ. CA3 retrieves coherent representations from degraded input: direct evidence for CA3 pattern completion and dentate gyrus pattern separation. Neuron 2014;81(2):416–27.
13. Gilbert PE, Kesner RP, Lee I. Dissociating hippocampal subregions: a double dissociation between dentate gyrus and CA1. Hippocampus 2001;11:626–36.
14. Hunsaker MR, Rosenberg JS, Kesner RP. The role of the dentate gyrus, CA3a, b and CA3c for detecting spatial and environmental novelty. Hippocampus 2008;18(10):1064–73.
15. Leutgeb JK, Leutgeb S, Moser M-B, Moser EI. Pattern separation in the denate gyrus and CA3 of the hippocampus. Science 2007;315:961–6.
16. Musso N, Kesner R. A role for the dorsal dentate gyrus in color context pattern separation. Neurology 2015;84(14). Supplement:S49-001.
17. Weeden CS, Hu NJ, Ho LU, Kesner RP. The role of the ventral dentate gyrus in olfactory pattern separation. Hippocampus 2014;24(5):553–9.
18. Goodman J. Grocery shopping: Who, where and when. Timeuseinstitute.org 2008; accessed Dec 2016.
19. Statista.com. Consumers’ weekly grocery shopping trips in the United States from 2006–2016 (average weekly trips per household). Statista.com 2016 (accessed 12/12/16).
20. Lee RB, DeVore I, editors. Man the hunter. Transaction Publishers 1968;2009.
21. Brochet F, Morrot G. Influence of the context on the perception of wine cognitive and methodological implications. OENO One 1999;33 (4):187–92.
22. Kohli C, LaBahn DW. Creating effective brand names: a study of the naming process. J Advert Res 1997;37(1):67–75.
23. Lyons DM, Yang C, Sawyer-Glover AM, Mosely ME, Schatzberg AF. Early life stress and inherited variation in monkey hippocampal volumes. Arch Gen Psychiatry 2001;58:1145–51.
24. Gilbertson MW, Shenton ME, Ciszewski A, et al. Smaller hippocampal volume predicts pathologic vulnerability to psychological trauma. Nat Neurosci 2002;5(11):1242–7.
25. Gianaros PJ, Jennings JR, Sheu LK, Greer PJ, Kuller LH, Matthews KA. Prospective reports of chronic life stress predict decreased grey matter volume in the hippocampus. Neuroimage 2007;35(2):795–803.
26. Geuze E, Vermetten E, Bremner JD. MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders. Mol Psychiatry 2005;2005(10):160–84.