In the spring of 2008, engineers at information technology company Hewlett-Packard jumped for joy. They had succeeded in building a new electronic circuit component called a memristor, a kind of resistor with memory that significantly speeds up computer start-up and other tasks. And this from a component measuring only five nanometers (a millionth of a millimetre, eds.) sandwiched between two layers of platinum – a nanotechnology marvel.

But equally remarkable to the engineering of this ‘missing link in electronics’ was its conceptualisation some 37 years earlier, when Professor Leon Chua (pictured left) articulated the memristor’s theoretical existence. For a long time, this discovery was compared to the missing elements in Mendeleev’s periodic table. “I didn’t think I would live to witness it’s actualisation,” said Chua in a 2008 interview in Nature.

Since then, the memristor has been used as a model for brain functioning, particularly the behaviour of neurons and memory. “My main ambition is to try and find the mechanisms behind human intelligence and build electronic circuits that emulate that intelligence,” he explains. “This implies finding electronic components that emulate the synapse and the axon, the two fundamental building blocks of neurons. The memristor turns out to be exactly the missing link in this story. There are two types of memristor: the first – the locally passive – emulates the synapse, the second – the locally active – matches the axon.”

The theories lead to intriguing innovations. “They enable us to build brain-like machines. The hardware is there, but we also need the software.” Chua was able to bridge this gap as well: “I have developed a new theory, called ‘the principle of local activity’. A special case of that, called ‘the edge of chaos’, is precisely the explanation of how human intelligence arises.”

Mystery

Despite the memristor’s success, Chua sees his ‘edge of chaos’ concept as his most significant contribution. “In my opinion, it is the third law of thermodynamics and it is responsible for almost anything that is intelligent, exciting or creative in this world. It explains how complexity arises, in economic bubbles, social unrest or revolutions, for instance. How does such a thing arise from small units or individuals? Well, exactly because of this principle of local activity.” Shunning retirement, Chua is determined to continue working on the idea for many more years to come. “This will be disruptive. It will alter our insight forever, both in our thinking and in the building of machines.”

Chua’s Hungarian counterpart and long-time collaborator, Tamás Roska (pictured left), agrees. The two men have been collaborating for more than thirty years. Roska’s work builds on Chua’s theory of non-linear circuits and cellular networks. Together with Chua, he developed the Cellular Neural Network Computer (CNN). “The CNN is a computer architecture that drastically differs from the classical, digital computers,” Roska explains. “This kind of architecture is defined by two things: a geometrical grid of cells, and an instruction on how the cells interact. This instruction will make the grid of cells dynamically evolve in a spatio-temporal wave. By performing several of these elementary instructions one after the other, a CNN can achieve a complicated task on an image. This is again based on the way our brain works. It’s a thing that has fascinated me for years.”

In the brain, neurons work in a parallel and interactive way. This is reflected in Chua’s and Roska’s mathematical architectures, in which millions of components on each electronical chip can fulfill tasks simultaneously, and consequently are capable of executing more tasks in a shorter period of time. In a classical computer structure, components spend a lot of time waiting for one another.

“Actually, I’m becoming more and more cautious and humble when talking about the brain – as a whole it’s still kind of an enigma. One of the particularly good things to come out of this research was our collaboration with outstanding neuroscientists. This has deeply informed our understanding of image flow processing in the brain and that is very encouraging.”

Adventure

Indeed, Roska is most lauded for his breakthroughs in real-time image processing. “The CNN proved to be very useful in partially mimicking the visual pathway, in particular the retina and the visual cortex. Based on our insights, our team was able to develop a new kind of computer.” The applications are numerous: real-time image processing tasks in navigation, bionic eyeglasses, collision avoidance of unmanned aerial vehicles, mission-critical operations, etc. Roska’s team has also implemented the technology in tactile and auditive applications.

“The first visual microprocessors are already on the market and I predict that sensory computers will become ubiquitous. The computer architectures of the future will increasingly be cellular and – perhaps even more interesting – molecular-level computing is emerging as well.”

In the coming years, Roska wants to devote himself to these emerging technologies, as well as to ‘bionic systems’, a new field that has emerged at the crossroads of information technology, electronics, computing and biotechnology. “It is another adventure. Within a few years, many of today’s medical technologies will be replaced by these systems. We have already seen the emergence of a kind of brain pacemaker: it sends signals from the pacemaker to specific zones in the brain to block pain signals or stop involuntary movements caused by Parkinson’s disease, for instance. We want to process these signals in a more sophisticated way.”

Second home

Chua shares this revolutionary vision of the future. “Using memristors as the building blocks, we will be able to build brain-like machines. People will be able to talk and interact with these machines, which will use their intelligence to think on the spot and will be able to adapt themselves to many situations because of their intelligence. They will become ubiquitous and change our lives and thinking. I’m optimistic: I think this paradigm shift will play out within the next twenty years.”

In the meantime, this pioneering duo will be in Leuven to accept their joint honorary doctorate. “I feel especially grateful and honoured that it is the KU Leuven bestowing this distinction upon me,” says Roska. “I have been working closely together with Professor Joos Vandewalle and other Leuven professors in an atmosphere that is, scientifically and intellectually, one of the most outstanding in the world. After the collapse of the communist system, my rector and I visited Leuven and noticed how the Collegicum Hungaricum there had become an important refuge for many young people who had left Hungary after 1956. I have close connections with several universities, but the KU Leuven is especially dear to my heart.”

Chua is moved as well – although KU Leuven is certainly not the first to single him out for an honorary degree. “KU Leuven is one of the leading universities in Europe. Some call it the MIT of Europe, so this doctorate is an honour for me. I, too, have had good interactions with professors in Leuven, including Professor Joos Vandewalle, and I have visited Leuven on several occasions. It almost feels like a second home.”

LEON CHUA °1936, Chinese but born in Tarlac, the Philippines

Graduate of Massachusetts Institute of Technology (1961)

Professor Emeritus at the Department of Electrical Engineering and Computer Science at the University of California, Berkeley

Father of the theory of non-linear circuits and cellular neural networks

First to describe the existence of the 'memristor'