Troy, N.Y. — The latest edition of the Oxford English Dictionary boasts 22,000 pages of definitions. While that may seem far from succinct, new research suggests the reference manual is meticulously organized to be as concise as possible — a format that mirrors the way our brains make sense of and categorize the countless words in our vast vocabulary.

“Dictionaries have often been thought of as a frustratingly tangled web of words where the definition of word A refers users to word B, which is defined using word C, which ends up referring users back to word A,” said Mark Changizi, assistant professor of cognitive science at Rensselaer Polytechnic Institute . “But this research suggests that all words are grounded in a small set of atomic words — and it’s likely that the dictionary ’s large-scale organization has been driven over time by the way humans mentally systematize words and their meanings.”

Dictionaries are built like an inverted pyramid. The most complex words (e.g., “albacore” and “antelope”) sit at the top and are defined by words that are more basic, and thus lower on the pyramid. Eventually all words are linked to a small number of words — called “atomic words,” such as “act” and “group”) — that are so fundamental they cannot be defined by simpler terms. The number of levels of definition it takes to get from a word to an atomic word is called the “hierarchical level” of the word. Changizi’s research, which was published online this week and will appear in the June print edition of the Journal of Cognitive Systems Research, indicates that the dictionaries we use every day utilize approximately the optimal number of hierarchical levels — and provide a visual roadmap of how the lexicon itself has culturally evolved over tens of thousands of years to help lower the overall “brain space” required to encode it, according to Changizi.

Many other human inventions — such as writing and other human visual signs — have been designed either explicitly or via cultural selection over time so as to minimize their demands on the brain, Changizi said. By conducting a series of calculations based on the estimation that the most complex words in the dictionary total around 100,000 different terms, and that the number of atomic words range from 10 to 60, Changizi was able to devise three signature features present in the most efficient dictionaries — as well as in their human counterpart, the brain. Most importantly, he discovered that the total number of words across all the definitions in the dictionary (and thus the size of the dictionary) changes in relation to the total number of hierarchical levels present. Optimal dictionaries should have approximately seven hierarchical levels, according to Changizi.

“The presence of around seven levels of definition will reduce the overall size of the dictionary, so that it is about 30 percent of the size it would be if there were only two hierarchical levels,” Changizi said. Additionally, users will find that there are progressively more words at each successive hierarchical level, and that each hierarchical level contributes mostly to the definitions of the words just one level above their own, according to Changizi, who put his three predictions to the test by studying actual dictionaries.

The Oxford English Dictionary and WordNet — a large, online lexical database of English, developed at Princeton University — were found to possess all three signatures of an economically organized dictionary, and thus were organized in such a way as to economize the amount of dictionary space required to define the lexicon, according to Changizi. “Somehow, over centuries, these revered reference books have achieved near-optimal organization,” Changizi said. “That optimality can likely be attributed to the fact that cultural selection pressures over time have shaped the organization of our lexicon so as to require as little mental space and energy as possible.”

Changizi believes his research has potential applications in the study of childhood learning, where scientists could analyze how students learn vocabulary words and possibly develop ways to optimize that learning process.

The classic model of how brain cells communicate was put forth in 1943 by Warren McCulloch and Walter Pitts, at the time the first digital computers were being envisaged, and the McCulloch-Pitts model suggested that brain cells communicate in a binary fashion, represented by a “1” for firing and a “0” for not firing, much as a modern computer functions.

While it is common to say that a mammalian brain functions like a computer, this is a somewhat faulty idea, in part because the observation from the Traub lab suggests that gap junctions cause “short circuiting” as part of the brain’s normal functions. A real computer could not function if it short circuited. It is possible that these short circuits in the mammalian brain generally enhance brain function and adaptation to the environment, such as by permitting creative thinking, the combining of isolated facts into new ideas.

Researchers have found strong evidence for a novel type of communication between nerve cells in the brain. The findings may have relevance for the prevention and treatment of epilepsy, and possibly in the exploration of other aspects of brain functions, from creative thought processes to mental illnesses such as schizophrenia.

Human interaction and stimulation enhance chimpanzees’ cognitive abilities, according to new research from the Chimpanzee Cognition Center at The Ohio State University. The study (1) is the first to demonstrate that raising chimpanzees in a human cultural environment enhances their cognitive abilities, as measured by their ability to understand how tools work.

The scientists compared three groups of chimpanzees: one with a history of long-term stable, social interaction with humans (‘enculturated’); a group raised in a sanctuary setting, with only caretaker contact with humans (‘semi-enculturated’); and another group raised under more austere captive conditions (laboratory chimpanzees). The experiments looked at how the chimpanzees used rakes in order to retrieve a fruit yoghurt reward. The overall study examined not only whether the chimpanzees understood the properties of the tool, but also whether they understood the reasons why the tool worked.

The researchers gave the animals access to small rakes with either a rigid wooden head or a flimsy fabric head. Both enculturated and semi-enculturated chimpanzees correctly chose the rigid rake which enabled them to obtain the reward, indicating that both of these groups understood the physical properties of the two different rakes.

The researchers then presented the same two groups with two identical ‘hybrid’ rakes. Each rake head had a rigid side made of wood (functional) and another side made of flimsy cloth (non-functional). The reward was placed in front of the rigid side of one rake, and in front of the flimsy side of the second rake. The animals who picked the rake with the food reward on the rigid side demonstrated that they understood the causal principles behind the functionality of the rake.

The enculturated chimpanzees successfully selected the functional rake, while the sanctuary chimpanzees chose randomly between the two hybrid tools. The captive laboratory chimpanzees failed both tests, as demonstrated in previously published work (2).

According to Dr. Sarah Boysen, who led the study, “We think our findings mean that the conditions under which chimpanzees are raised, housed, and maintained have long-term effects on their cognitive development, and offer direct comparisons with early experience, issues of attachment, and preschool education for human infants and children,”

The authors conclude that the differences in performance between the three groups are directly attributable to the significant effect of level of enculturation. They add that “enculturated chimpanzees may be better at learning within a highly social, interactive context because they have heightened attention to the actions of others.”

1. Furlong EE, Boose KJ, Boysen ST (2007). Raking it in: the impact of enculturation on chimpanzee tool use. Animal Cognition DOI 10.1007/s10071-007-0091-6

2. Povinelli DJ (2000). Folk physics for apes: the chimpanzee’s theory of how the world works. Oxford University Press, New York.

Source: Animal Cognition

A newly discovered interplay of cells in one of the brain’s memory centers sheds light on how you recall your grocery list, where you laid your keys, and a host of important but fleeting daily tasks.

Scientists at Weill Cornell Medical College say their experiments with common goldfish are uncovering the secrets of a form of short-term recall known as “working memory.”

“We’ve now identified a mechanism that can organize the activity of groups of cells involved in this important form of recall,” says lead researcher Dr. Emre Aksay, assistant professor of computational neuroscience in the HRH Prince Alwaleed Bin Talal Bin Abdulaziz Al-Saud Institute for Computational Biomedicine at Weill Cornell Medical College in New York City.

“Furthermore, because deficits in working memory are often a precursor of schizophrenia, drugs that target this mechanism might someday help fight that debilitating disease,” he says.

The findings have been published in Nature Neuroscience.

Humans rely on their working memory every day to keep track of faces and names, tasks at school or in the workplace, and other important bits of information. “This process is distinct, neurologically speaking, from the storage and retrieval of longer-term memories,” explains Dr. Aksay, who is also assistant professor of physiology and biophysics at Weill Cornell.

Experts in labs around the world have developed theories as to how this process works. “Its basis lies in the ability of specific neurons to maintain a level of activity in the absence of input — a persistent firing rate — that’s finely coordinated across related groups of cells,” Dr. Aksay says.

But how do these brain cells communicate which each other to coordinate this activity”

To find out, Dr. Aksay, along with colleagues Dr. David Tank of Princeton University, and Dr. Mark Goldman of Wellesley College, turned to the common goldfish.

“It’s really quite difficult to test the function of individual brain cells in primates and higher animals during behavior, but the goldfish’s memory centers are much more accessible to research,” Dr. Aksay explains. “We looked specifically at the fishes’ oculomotor system — the neural circuitry that directs the fish to shift its eyes left or right based on stimuli in the local environment.” Because stimuli can be ever-changing and fleeting, the fish relies on its short-term memory to help guide these eye movements.

Two groups of cells are involved in this oculomotor memory, one in each half of the brain. Each group contains two types of neurons — inhibitory cells and excitatory cells, and it is the inhibitory neurons that allow the two groups to interact. “In our experiments, we used pharmacologic means to interrupt either excitatory or inhibitory pathways, and then we watched what happened to persistent firing,” Dr. Aksay says.

When the excitatory pathways were dampened, the persistence was impaired — suggesting that excitation is essential to the sustained firing that working memory requires.

“The real surprise came when we turned off many of the inhibitory pathways,” Dr. Aksay says. In that case, persistent firing remained, but was often present at inappropriate times.

“It appears that the inhibitory cells are not key or even required to generate persistent firing,” the researcher says. “Instead, they send a message from one group to the other that helps coordinate two sides: the role of inhibition in this system is to make sure that only one group is generating persistent activity at a given time. In this way, the goldfish doesn’t get a mixed signal telling it to move its eyes in both directions at once.”

This new finding has big implications for our understanding of the neural processes underlying working memory and the instantaneous decision-making that goes on based on that knowledge.

It might also have broader applications for psychiatric illness, Dr. Aksay notes.

“Many schizophrenic individuals, for example, show severe deficits in working memory, and children with working memory problems are at heightened risk of developing schizophrenia as adults,” he says. Dysfunction in key inhibitory pathways that link brain cells has long been associated with these problems.

“These findings suggest that it is necessary to address not only deficits in excitatory pathways that lead to a lack of persistent firing but also dysfunction in inhibitory pathways that lead to a lack of coordination among groups of cells,” Dr. Aksay explains. “This strategy could provide improved treatment options for people with schizophrenia.”

Source: New York- Presbyterian Hospital/Weill Cornell Medical Center/Weill Cornell Medical College