MD-Writer Blog

Two articles last month describe the relationship between inner mental worlds and the activity of specific neurons in the region of the brain called the hippocampus. But one article reports an experiment with rats and the other with humans.

The first piece in the Journal Neuron was reported in ScienceDaily. Researchers at the University of Minnesota Medical School recorded the brain activity in the hippocampus—where memories are formed—of rats trained on a maze to learn to follow two routes, designated A and B, to obtain food.

The rats wore electrode hats while they learned the maze. The scientists pinned down which hippocampal neurons, called “place cells,” fired in association with locations along each route. And they determined the firing sequences of the place cells for each route.

They got a surprise when the place cells firing while the rats were moving along one route weren’t necessarily the ones associated with that route. The following is from the ScienceDaily report:

The researchers found that the animals would replay sequence B more often, even when they spent most of their time running sequence A. In other words, the researchers found that the rats were most likely to replay the path they had experienced less often. … [Also, they] were able to observe the animal making connections between paths that it had never physically traveled before. For example, if the animal had physically traveled from point A to point B, and from point B to point C, but never from point A to point C, they observed the single sequence A to B to C during the replay process, implying that the rat’s brain was able to make the connection between points A and C on its internal map.

Neuroscientists at University College London performed the human experiment, which was published in Cell Biology and reported in Science online. They obtained fMRIs of the subjects hippocampuses rather than use electrodes. These real time, high resolution fMRIs recorded regional blood flow, which is assumed to reflect neuronal activity.

The researchers showed the volunteers three 7-second movies of an actress doing simple things, such as dropping a letter in a mailbox. The subjects were asked to memorize what they saw. They recorded the fMRIs of each subject while this was happening. Later the subjects were asked to choose one of the movies and recall it, while also undergoing fMRIs.

A computer, programmed with an algorithm to analyze the fMRIs, was able to determine which movies the subjects were remembering. In other words, using the algorithm, the computer had correctly picked out which neurons fired in association with which internal scene.

In my view, the two studies—in two different species of mammals—found approximately the same thing. Both studies provided evidence of the creatures’ mental worlds. And both support the notion that the mental projection of internal representations is associated with the activities of hippocampal neurons, a region of the brain known to work with memories.

For some of us humans, the most astonishing aspect might be the evidence provided that rats have mental worlds just as humans do.

I once participated in a discussion lasting more than a year in one of the first online threads. It began before the turn of the millennium and was hosted by the NY Times. The thread was titled “Explaining Consciousness,” and during a portion of its existence, I debated another participant who posted under the tag “ottoworks.” Otto did not believe any species but humans could have conscious mental worlds. He thought consciousness required the faculty of language as a prerequisite. I differed and thought that many animals have consciousness and human consciousness is not unique in the animal kingdom.

I still think that. Much of neurocognitive science in the years since has, I think, tended to support my view.

Neuroscientists have demonstrated that the focusing of attention in consciousness is associated with specific frequencies of neuronal activity in the brain, and anticipation of an event requiring attention is associated with other specific frequencies.

The researchers, at the University of Chicago, Baylor College of Medicine, and Rush University, showed that one person’s conscious attention to instructions displayed on a computer screen was signaled by the onset of beta oscillations (12-30 Hz) of local field potentials in his motor cortex. They also demonstrated that delta oscillations (0.5-1.5 Hz) in the same region indicated the subject’s enhanced readiness to focus attention on an anticipated instruction.

The research was reported last Thursday in the journal Neuron. An article on the findings appeared in ScienceDaily the next day.

The subject of the experiment was a quadriplegic person, whose brain had been implanted with a computer chip holding an array of 100 electrodes. The device allows paralyzed individuals to control the motion of a computer cursor with their brain. However, the chip also permits recording of local field potentials similar to brain waves on an EEG.

In the experiment the subject watched a rhythmic sequence of five instructions to move the cursor, as they appeared on the computer screen. But the person was told to carry out only the second and fourth instructions. The recording from the electrode showed that the amplitude of beta frequency brain waves increased as the subject waited for the relevant instructions to appear, and the beta amplitude peaked just before they did. The beta amplitude subsided between the relevant instructions, when the subject was ignoring the other instructions not performed.

The electrode recordings also showed that the amplitude of delta frequency waves entrained to a periodicity that followed to the timing of the appearance of the instructions. The scientists inferred that the delta waves play a role in enhancing a readiness to pay attention, so that maximum beta activity would coincide with the appearance of the anticipated input.

The relationship of the two frequencies is like the melody and bass of a tune, one scientist explained. “The slow rhythm is kind of like the rhythm section, and you anticipate notes at particular moments in time based on that slower rhythm,” he said.

The researchers hope that the ability to track a person’s attention could help people to improve their concentration. In the case of paralyzed people connecting with computers, attention monitoring might help to improve their control of the computer.

The discovery also clarifies an important issue regarding the nature consciousness. Brain scientists sometimes fail to distinguish between consciousness, an inclusive concept, and attention, a specific function of consciousness. For example, we sometimes say that we become conscious of a particular feeling or thought. We don’t mean that we are not already conscious, but rather a feeling or thought comes to our attention—we notice it.

An article touching on this issue appeared last December in Scientific American. Daniel Bor, a neuroscientist and author of the report, wrote in a comment: “Some researchers suggest that attention and consciousness are one and the same, in fact. A very interesting question.”

The new research points to the answer by demonstrating that particular brain waves in the beta frequencies are associated with the function of attention. Yet the contemporaneous occurrence of delta waves also shows that consciousness is present, whether or not the function of attention is engaged. (Of course, the fact that the subject was alert and responsive (conscious) during beta amplitude troughs also shows that consciousness is distinct from attention.)

This difference was graphically illustrated in the first episode of the Charlie Rose’s remarkable series of programs on brain research. One of the brain scientists, Tony Movshon, used the Necker cube to demostrate that the brain can synthesize two alternative perceptions of one diagram of a cube. In experiencing this familiar but striking optical illusion, we discover that as we shift our function of attention, we see one version of the cube, then the other. But our function of consciousness remains with us all the time, and the two perceptions occur within our one consciousness.