Tag Archives: navigation

The smell of the land

The sense of smell is intriguing. It is not as readily conscious as sight, hearing, touch and taste; so it is often discounted. However, humans do have the ability is smell quite well and can learn to do so in sophisticated and conscious ways. Perfumers are an example of this. We also know that a particular smell can bring back the memory of a place in a flash that seems quite miraculous. It is the most important sense for many mammals – used to identify objects and places, track and navigate, and communicate emotional signals. There is no reason to think that we are that much different; we probably use smell as a background (largely unconscious) canvas on which to perceive the world.

Recent research (citation below) has indicated such a canvas. Jacobs and others experimented with human subjects to see if they could map their surroundings using odour gradients. They used a large room with two distinct sources of different odours. The subjects were disoriented, placed in a spot and asked to remember its smell. They were disoriented again and asked to find the spot using their memory of the odour. This was done first with sight and hearing blocked and only the sense of smell available, then repeated with sight as the only sense available, and finally with all three senses blocked. The subjects could come close to the target spot with scent alone, compared to the control of none of the three senses being available.

This is a distinct ability and not the same a tracking a smell or identifying an object or place. This is the formation of a map based on odour gradients. Spatial maps are created in the hippocampus and the olfactory bulb is strongly connected to the hippocampus. The authors address the relationship between the odour map, the sound map (echo location), and the visual map etc. “The ability to navigate accurately is critical to survival for most species. Perhaps for this reason, it is a general property of navigation that locations are encoded redundantly, using multiple orientation mechanisms, often from multiple sensory systems. Encoding the location with independent systems is also necessary to correct and calibrate the accuracy of any one system. As a general principle, then, navigational accuracy and robustness should increase with the number of unique properties exhibited by redundant orientation systems.

Abstract: “Although predicted by theory, there is no direct evidence that an animal can define an arbitrary location in space as a coordinate location on an odor grid. Here we show that humans can do so. Using a spatial match-to-sample procedure, humans were led to a random location within a room diffused with two odors. After brief sampling and spatial disorientation, they had to return to this location. Over three conditions, participants had access to different sensory stimuli: olfactory only, visual only, and a final control condition with no olfactory, visual, or auditory stimuli. Humans located the target with higher accuracy in the olfaction-only condition than in the control condition and showed higher accuracy than chance. Thus a mechanism long proposed for the homing pigeon, the ability to define a location on a map constructed from chemical stimuli, may also be a navigational mechanism used by humans.”

Citation: Jacobs LF, Arter J, Cook A, Sulloway FJ (2015) Olfactory Orientation and Navigation in Humans. PLoS ONE 10(6): e0129387. Doi:10.1371/ journal.pone.0129387

Ways to navigate

When I was a little girl, my father stood me on the door step and pointed across the yard and said, “that’s north”. He went on that the house behind me was south, the village was west and the grove of trees was east. To this day when I think of north I see the barn and so on; my sense of direction is based, even after 70 odd years, on the vision of the farm yard I grew up in. I have a small problem with left and right, but if I just think of facing the barn then left is in the west towards the village. Until I traveled away from the flat prairies, that was all I needed and the only skill required was to keep track of where north was. I found later that landmarks were useful and so was a map.

My husband has his own way of finding his way and never seems to worry about the cardinal directions. He does not seem to keep an continuous, unconscious tally of which way he is facing. His only way of dealing with cardinal directions is to know that the sun is going to be to the south and going from east to west during the day. (This was a problem when he was first in the tropics where the sun is not always to the south – he could get lost within half a city block.) I had never paid any attention to the sun to know which direction I was going – it had never occurred to me. It is clear to me that there is more than one way to navigate.

A recent paper (citation below) examines types of navigation. Head-direction cells in the entorhinal/subicular area have been known for some time. It appears to be why Alzheimer’s sufferers tend to lose their sense of direction early in the disease; one of the first areas affected is the entorhinal cortex. But heading cells alone cannot give navigation accuracy. What is needed is a goal-direction cell to work with heading to keep movement in the direction of the goal. And this directional information has to be framed in either a world view (north, south, east, west) or a self view (left, right, forward, back). The geocentric information appears to be processed in the entorhinal/subicular area, egocentric information in the precuneus region. Navigation could also be done by following a sequence of visible landmarks using the place cells of the hippocampus. All of these methods could and would be used depending on the circumstances.

The researchers looked for goal-direction cells using multivoxel pattern analysis. (The method used to try and guess which video someone was watching that caused the interest in ‘mind reading’ last year; or, as reported in a previous posting, the difference between physical and social pain.) They found that the direction of the goal is stored by the same cells as the direction the body is facing. These cells were in the entorhinal/subicular area and geocentric. The same cells could be used for both heading and goal direction. The exact way this is done was not clear in this study. “Due to the relatively poor temporal resolution of fMRI, we are not able to determine what the temporal dynamics of head-direction simulation may be. Our assumption is that head-direction populations are initially involved in representing current facing direction and then switch to simulation during navigational planning. However, other temporal dynamics, such as constant oscillation between facing and goal direction, would explain our results equally well. Thus, we remain agnostic regarding the precise temporal dynamics involved in head-direction simulation, which will have to be resolved with alternative methodological approaches.

Their findings are relevant to actual navigation. “We found a significant positive correlation between entorhinal/subicular facing direction information and overall task accuracy….These results therefore show that participants with a stronger representation of current heading direction are both more accurate and faster at making goal direction judgments in this task

Here is the abstract: “Navigating to a safe place, such as a home or nest, is a fundamental behavior for all complex animals. Determining the direction to such goals is a crucial first step in navigation. Surprisingly, little is known about how or where in the brain this ‘‘goal direction signal’’ is represented. In mammals, ‘‘head-direction cells’’ are thought to support this process, but despite 30 years of research, no evidence for a goal direction representation has been reported. Here, we used fMRI to record neural activity while participants made goal direction judgments based on a previously learned virtual environment. We applied multivoxel pattern analysis to these data and found that the human entorhinal/subicular region contains a neural representation of intended goal direction. Furthermore, the neural pattern expressed for a given goal direction matched the pattern expressed when simply facing that same direction. This suggests the existence of a shared neural representation of both goal and facing direction. We argue that this reflects a mechanism based on head-direction populations that simulate future goal directions during route planning. Our data further revealed that the strength of direction information predicts performance. Finally, we found a dissociation between this geocentric information in the entorhinal/subicular region and egocentric direction information in the precuneus.”

Chadwick, M., Jolly, A., Amos, D., Hassabis, D., & Spiers, H. (2014). A Goal Direction Signal in the Human Entorhinal/Subicular Region Current Biology DOI: 10.1016/j.cub.2014.11.001

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