Do females have different neurological software from males?

Prof. Dr Bob van Hilten: 'Abnormal plasticity is more common in women.'

Women are more able to multi-task, but they often suffer more from hyperactivity with Parkinson's, chronic pain, anxiety disorders and depression.  Prof. Dr J.J. van Hilten believes that the female nervous system has a different software.  He will deliver his inaugural lecture on 23 May.

Bob van Hilten is carrying out research into movement disorders in the area of neurology.  Last week he was still with his research group in New York, where they were invited as the only non-Americans to discuss setting up an international consortium in the field of research into the origin of Parkinson's disease.  Van Hilten is involved in research into two in themselves very different illnesses which share the common factor that they both exhibit movement disturbances: Parkinson's and dystonia. 

Different software?
Dystonia is a neurological condition which is characterised by involuntary muscle contractions which lead to slow, twisting movements or abnormal postures.  What is remarkable is that dystonia occurs much more frequently among women than men.  How can this difference be explained? 

Examples of dystonia.

Van Hilten: 'When carrying out a task such as listening to a story, for example, in women there are apparently many more brain areas active than in men.  Women are also better than men at simultaneously carrying out several tasks, something which is only possible if different nerve networks can be active without mutual disruption to functioning.' Hyperactivity with Parkinson's disorder, chronic pain, anxiety disturbances and depression occur much more frequently in women than men.  Van Hilten: 'The reason for this is as yet unknown.  Current indications seem to suggest that the nervous system of women has a different type of software than that of men.'  

Neuroplasticity
How does the nervous system work? Each individual has some hundred billion nerve cells, which are integrated into networks in a genetically determined, fixed system.  This is the original ' hardware'  with which each human being is equipped.

Nerve cell with contact points

Nerve cells communicate with one another via contact points known as synapses.  Each individual nerve cell can change the signal transfer at each contact point and can increase or reduce the number of contact points. The information transfer from one nerve cell to the other can therefore be weakened or strengthened.  This process is called neuroplasticity.  In this way, different software is continuously being run on the hardware, whereby stimuli or experiences from the environment play an important role.  

Use it or lose it
How dynamic this process is, is illustrated by the cerebral development of children. In the original hardware of a new-born baby, an average nerve cell has 2,500 contact points with other nerves.  By around the age of three years, as a result of the many stimuli to which the child is exposed, this number will have increased to 15,000.  After this, the number decreases with age, because little-used connections are weakened or abandoned: use it or lose it.

Learning from neuroplasticity
Neuroplasticity enables us to gain new knowledge and skills.  Learning to ride a bicycle, to type or to play tennis is only possible because of the new connections made between nerve cells.  As a result of neuroplasticity, healthy nerve cells are able to take over the function of nerve cells from a damaged area of the brain, which means that a certain degree of repair is possible.  

The characteristic posture of a Parkinson's patient. Parkinson's disease Parkinson's disease is a disease of the brain whereby nerve cells, particularly but not exclusively in the substantia nigra slowly die off.  Parkinson's is regarded as a condition with primarily motory disturbances, but the illness is much more complicated than this.  Patients with Parkinson's also suffer from dementia, depression, sleeping and waking disorders, disturbances of the olfactory system and disorders of the bladder, intestine and blood pressure regulation. In addition, the medication which is used to treat the motor disturbances give rise to new problems.  These might include hyperactivity, hallucinations, day-time drowsiness and in a small number of patients compulsive phenomena such as hypersexuality, gambling or excessive purchasing behaviour.  Van Hilten coordinates the Leiden Scales for Outcomes in Parkinson's disease (SCOPA) project and is scientific coordinator of TREND, the national Trauma RElated Neuronal Dysfunction consortium.

A person who loses his or her sight as a result of an accident or through illness, can by learning braille connect the wiring between the nerve cells for language and vision with nerve cells which are important for touch.  

Plastic is not always fantastic
But plastic is not always so fantastic,' according to Van Hilten. 'In recent years it has become apparent that neuroplasticity also has its disadvantages and can be responsible for different disorders.  In patients suffering from Parkinson's, for example, the receptors which the medication affects, can become over-sensitive. As a result, patients can suffer from hyperactivity or lowered blood pressure.  Dystonia, chronic pain, the tendency towards drug addition, anxiety disorders and depression can be expressions of abnormal plasticity.'  

Abnormal neuroplasticity
Abnormal neuroplasticity is more frequent among women and is caused by a combination of genetic and environmental factors.  Genetic factors make us more or less vulnerable to particular environmental factors. Environmental factors are experiences which the body undergoes, such as making a new movement, a physical trauma or exposure to particular medicines. Apart from gender, age is also an important risk factor for neuroplasticity.  The younger the patient, the more readily instances of abnormal neuroplasticity occur and spread.   

Women are apparently more vulnerable to developing expressions of abnormal plasticity.  There is as yet no explanation for this.  Van Hilten: 'Women's software apparently works differently from that of men.'

(20 May 2008/DH )