I went over to mum and dad's and together we looked at some of the family photos - their brain scans.

Mum was the first to have her head read. She had MRI images made on 27 September 2000. The reasons for this were rapid loss of memory and episodic falls. There was not much to see: no haemorrhage, no lesions, no age-related change. The phrase that I repeated to mum this afternoon was 'No significant intercranial abnormality is seen.' However, it is obvious that despite the lack of physiological evidence, things were not all right with mum. This period coincides with those mentioned by Rachel and Derek in which mum was noticeably more vague and forgetful.

She went back for CT scans on 11 February 2004. This time it was 'No focal intercranial abnormality is seen.' The crucial distinction between 'significant' and 'focal' is lost on me. The only development was that age-related changes were now evident, and one of these was an enlargement of the ventricles. The ventricles are the four quite large fluid-filled spaces within the brain. As brains atrophy, or shrink, three visible physical changes take place: they draw away from the inside of the skull, the folds in the surface of the cortex widen, and the ventricles enlarge. Mum's brain was starting to shows signs of atrophy, but not much.

The CT scans for dad were done on 29 March 2006. In the low-key language used by doctors to communicate with each other, the report said 'Age-related ventricular and sulcal prominence noted.'  This means that the ventricles and the sulci (the furrows on the brain surface) were widening. There were also signs of inadequate blood-flow (ischemia). Signs of atrophy were therefore more marked in dad than in mum.

A visual comparison shows that dad indeed has much more marked atrophy of the brain than mum does, despite his lesser mental deficits.

I got the scans out of their big envelopes and started taping them to the big window at the back of the lounge. Mum and dad gathered to look at the pictures and comment. Mum seemed to have a great time with this. She kept seeing funny faces in the images, clowns, poodles, etc. Dad looked at some of his own scans, 'I can't see a brain there,' he said, quite seriously. 'Now you have to face up to what people have been telling you all along, dad,' I said.

Putting matching slices from mum and dad together shows the difference. Dad's brain seems to be swimming in a lot of space, whereas mum's is still quite a fat-looking thing filling out the skull. I mentioned this. Mum was not sure whether I was insulting her. It probably sounded like I was calling her a fat-head.

So, back and forth along the window they shuffled. By the time they got to the end they'd forgotten what they'd seen at the beginning. Mum kept pointing to her own name, repeated on every one of her images. Dad kept marvelling at the science, technology, and imagination that produces images of things that are enclosed and unseen. I have to agree with him on this one. One of the more recent innovations is that images are also supplied on CD, with a customised viewer that allows you to do fly-throughs and rotations. I had some time to play with the viewer this afternoon, but I shall be taking it home with me for another investigation later.

It's the next best thing to having an ancestor's skull on my desk.