The Leiden University Medical Center (LUMC) has recently cited prof. Semenza’s work on their monthly newsletter. Here is the excerpt:

How brain damage can elevate a politician to an icon

by Gert van Dijk and Roelien Bastiaanse

Brain damage can evoke odd, sometimes bizarre changes in cognitive functioning that fascinate everyone. Neurologists were among the first to share that fascination of such ‘experiments of nature’ and used the powers of observation and analysis to increase knowledge of how the brain works. Over time, neurologists somehow either lost interest in the subject or no longer allowed themselves the time to sit and think, so it fell to others to study these particular observations, which are pearls for science while being disasters to patients.

One of these others is Carlo Semenza, a psychiatrist working as a neuropsychologist. Semenza, just retired from the University of Padua, is the king of ‘category-specific deficits’. These deficits arise after brain damage and affect one category whereas other categories remain intact. Such a ‘category’ can be a word class (e.g., verbs impaired, nouns intact), a semantic category (e.g., representations of living things impaired, of non-living things intact) or a cognitive domain (e.g., reading impaired, writing intact).

For instance, Semenza described a patient with acalculia, meaning a deficit of calculations. The patient had impaired addition, subtraction and multiplication of numbers consisting of multiple digits, but division was intact. So, he calculated 230:17 correctly, but made errors with 230×17.

Perhaps you should stop reading now, sit down and think hard: what is it that distinguishes division from the other arithmetic processes?

The explanation Semenza and colleagues found is as simple as it is ingenious: addition, subtraction and multiplication are operations done from right to left, whereas division is done from left to right. This explanation was proven by the patient’s error pattern. When we add two multiple digit numbers, we start on the right and if the sum is larger than 9, we carry the 1 and add it to the following two digits. The errors of the patient showed that he started on the left for all calculations: this leaves division intact, but other calculations become impaired.

Our favourite case described by Semenza and colleagues is a patient with semantic dementia who had prosopagnosia (an inability to recognize faces). This woman could not name pictures of famous people. When asked whether she could tell who these persons were or what their occupation was, she was only able to provide very vague information. She did recognize a picture of the pope, but made no distinction between the present and previous popes; she just recognized the outfit. She also recognized Christ on the cross. According to the authors, the pope and Christ on the cross were regarded by the patient as belonging to the category of ‘icons’, not the one of ‘persons’. There was one remarkable exception, though: the patient recognized a picture of Berlusconi correctly. When asked who the man was, the patient said that he was very rich, a television network owner and a politician. When her dementia increased, she was no longer able to recognize her children or her neighbours. However, she still recognized the pope, Christ on the cross and Berlusconi from pictures. The authors state that “repeated exposure due to propaganda may have turned Berlusconi’s face into a non-living, but very well recognizable item” (Mondini & Semenza, 2006, p 334).

So the patient did not recognise the man Berlusconi as a living breathing person, because her brain had lost the facility to process that category; but because the category ‘icons’ was still processed adequately, she came up with the correct description. Fascinating, isn’t it?

Such cases are a reminder that clues to how the brain works are hidden in the cognitive consequences of brain damage, waiting for curious neuroscientists to bring them to light, using nothing more complex than observation and deep thought.

Chiarelli, V., Menichelli, A, Zadini, A & Semenza, C. (2011) Good division, but bad addition, subtraction and multiplication: A “leftmost-first” bug? Cortex, 47, 250-258

Mondini, S. & Semenza, C. (2006) How Berlusconi keeps his face: A neuropsychological study in the case of semantic dementia. Cortex, 42, 332-335.