Roughly two or three times a year, I get a letter or email out of the blue from a former student.

The minority want something. It might be a reference ¨C not easy to provide for someone you taught in a class of 80, or even a seminar of six, over 30 years ago. Some are having a career change and want advice. And some want you to help their children get into a ¡°good university¡±.

But the vast majority seem simply to want to thank me. Many express surprise that I (immediately) reply. Most say that they were probably not a very good student but that I lit a small candle in their imagination that still burns. Some proudly tell me one of their children is now studying psychology. A number went on to do postgraduate degrees themselves.

Their letters, in the main, are not very long, though a few quote examples of a lecture or incident they recall. They liked, in particular, my self-disclosure and the case studies that I rambled on about. They remember what psychologists call ¡°Aha experiences¡±.

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Where possible, I arrange to meet them. As a result, one or two are now friends. Others just ¡°say their piece¡± and move on. Either way, I am very grateful. Receiving their letters is one of the greatest perks of the academic life.

Of course, there is nothing uniquely magical about my teaching. Talk to students about why they chose their particular subject and 90 per cent credit a very particular teacher. I have always thought the best index of teaching skills is the number of scholars who pursue the discipline, in one way or another, after school.

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I have also penned my own fair share of letters to lecturers who had a long-lasting effect on me. But finding their contact details has not always been easy given that I went first to university in my native South Africa, emigrated to the UK when I was 22 and am now over 70.

In particular, I have been struggling for many years to find a contact address for my third-form English master, Keith Chick. He gave me an abiding love of poetry. I still have the textbook, The Poet Sings, annotated in pencil. I turn to poetry when distressed as a first refuge and am instantly calmed. It is, in my experience, far better than pills or booze, and often as good as the ¡°talking therapies¡±. And yes, I particularly like the non-PC poets like Kipling, de la Mare and Rossetti.

I don¡¯t know what Mr Chick did or how he did it. Subsequent teachers and lecturers succeeded as he did. So I have spent hours on the web trying to track him down. I have discovered that he left schoolteaching and ended up as a professor of linguistics. I have read a few of his papers, as well as a eulogy on his retirement. He must be in his mid to late eighties now, but I still feel the need to thank him ¨C profoundly.

But why? It isn¡¯t just out of a sense of obligation. The expression of gratitude is not just a profoundly enriching experience for the object of that gratitude: the same is true for the person who expresses it.

The ¡°father of positive psychology¡±, Martin Seligman, first suggested the emotional benefits of counting our blessings 20 years ago, and some reasonably good subsequent research, with appropriate experimental designs, suggests that those benefits are long-lasting.

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Of course, religious believers already know that feeling grateful, even blessed, has profound consequences. But gratitude towards our fellow mortals is an even better stress suppressor than gratitude towards a heavenly father.

For those to whom this mindset doesn¡¯t come naturally, positive psychologists suggest ¡°grateful recounting¡±, which involves cultivating a habit of remembering and reflecting on good things in your life. This can be facilitated by regularly recording what you are thankful for in a structured ¡°gratitude journal¡±. Another technique is ¡°grateful reappraisal¡±, an exercise that asks you to recall a negative or difficult experience and reflect on it in a new light.

Expressing gratitude is cheap ¨C and, via letters or diaries, relatively easy even for the emotionally repressed. So why not do it more?

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Yes, I know. Too schmaltzy, too American. A waggish friend of mine, hearing me wax lyrical on the joys of gratitude letters, even went so far as to suggest, instead, sending letters of loathing/disappointment/anger to those tedious, obsessional, hypercritical bastards who destroy your interest and passion in their subject. Another friend and I, over too many glasses of red wine, actually composed such a letter to a lecturer we had in common. It was a lot of fun, particularly thinking of those very English subtly barbed phrases, such as ¡°you took no prisoners¡± and ¡°alas, I did not continue with whatever´Ç±ô´Ç²µ²â¡±.

But you soon learn that revelling in bile really doesn¡¯t work. It is a bit like swearing or cussing: it may have a short-term cathartic effect, but the emotional benefits certainly don¡¯t endure. Perhaps that is a good thing.

So here is your homework exercise. Think of a teacher and/or a lecturer who ¡°lit your flame¡±, ¡°floated your boat¡± or profoundly excited your interest in a subject you pursued and still feel passionate about. Write a gratitude letter. Now.

It is the cheapest and most effective therapy there is. And, I promise you, they will be chuffed.

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Adrian Furnham, currently a professor in Norway, still lectures students.