A PhD from two universities on drug abuse

Stimulating drugs, such as khat and cocaine, have a negative impact on everyday activities such as driving a car and working, as well as on social behaviour. That’s because these drugs seriously damage control centres in a user’s brain. Psychologist Manuel Ruiz’s research aims to increase understanding, and improve treatment, of drug addiction. His PhD defence at both Leiden University and the University of Granada took place on May 12.

Combining the best of two universities

Manuel Ruiz working on an experiment

Manuel Ruiz working on an experiment

Ruiz is the personification of the collaboration between Leiden University and the University of Granada, as he is the first PhD candidate to be given a doctor’s title from both universities. ‘That collaboration agreement enabled me to combine the best of both of these renowned universities,’ Ruiz says. As part of the research team of cognitive psychologist Bernhard Hommel, he studied the influence of khat and cocaine on the basic mechanisms governing our thinking and actions. In various experiments he monitored khat and cocaine users working on a number of cognitive tasks on computers, all of which revolved around suppressing actions, mental flexibility or updating your memory. These mental processes stimulate information processing in the brain.

Similarities between khat and cocaine addictions

‘I’m especially interested in human cognition and the mental processes that focus on problem solving and the making of quick decisions,’ Ruiz explains. ‘But drug use influences those processes and I wanted to find out how great that effect is.’ He therefore devised a series of cognitive tasks that revealed the similarities between khat and cocaine use. The research question he was trying to answer consists of two components. Firstly, he wanted to conduct the first-ever scientific study of the effects of regular khat use on thinking and action processes. As the lack of control in those areas is well known in cocaine users, Ruiz also wanted to test language and memory processes of addicts.

Understanding and treating drug addition

Ruiz: ‘My research revealed important implications that could be used to increase understanding, and improve treatment, of drug abuse. The discovered similarities in the mental processes of khat and cocaine users is very important, because using these drugs will seriously damage your daily functioning, including your ability to drive a car and function in a work environment, and will even affect your social skills. My detailed description of these effects are also seen as an important tool that will hopefully help khat and cocaine users to decide to quit, and to stay clean as well.’

The future of synthetic drugs

In the future, Ruiz wants to focus on the possible cognitive defects users of synthetic drugs suffer from, as these are easy to find and purchase online. Ruiz: ‘Over the last decade, a new type of drug has arrived on the scene. A drug that people use without knowing the short- and long-term effects it has on their brains.’

PhD defence: M.J. Ruiz Muñoz
Controlling thought and action: a perspective from khat users and cocaine users

PhD supervisor:
Prof. B. Hommel

Read more

Leiden Institute for Brain and Cognition (LIBC) Blog
Cocaine consumption impairs language production - Manuel Ruiz

(13 May 2015)

Studying in Leiden



Last Modified: 13-05-2015