Testing procedures and populations

The types of test used to assess different domains of very long term memory vary between the studies examined, so the tests used for each domain will be considered and the results obtained from them, as well as what this could mean.

Verbal recall and recognition were tested by two main groups of tests: stories and word lists. Stories were used in 7 studies (Blake et al., 2000; Manes et al., 2005; Bell, 2006; Mameniskiene et al., 2006; Davidson et al., 2007; Butler et al., 2009; Wilkinson et al., under review), with three testing recognition as well as recall. The story used most commonly was one of the logical memory stories in WMS-III, or a modified version of it. Also used were the story subtest of the Children‟s Memory Scale, stories from the Adult Memory and Information Processing Battery and a prose

testing verbal recall of a story (Bell, 2006) failed to demonstrate accelerated forgetting in patients, using the WMS logical memory story. In those testing recognition memory of stories, one found accelerated forgetting over a period of 8 weeks (Blake et al., 2000) while two found no difference between groups over one and two week intervals (Bell, 2006; Davidson et al., 2007).

A word list was used to assess verbal recall in five studies (Martin et al., 1991; Bell et al., 2005; Mameniskiene et al., 2006; Butler et al., 2007; Butler et al., 2009) as well as verbal recognition in one (Martin et al., 1991). 15 words from the Rey Auditory Verbal Learning Task or an equivalent were used in three of these, and 12 words from the Selective Reminding Test in the other two studies. Again, accelerated forgetting was demonstrated in patients for verbal recall in all studies bar one (Bell et al., 2005), but was not found in verbal recognition (although this was only examined in one study). Stories and word lists both seem to show similar evidence of verbal long term forgetting.

Non-verbal recall and recognition were tested in eight studies (Giovagnoli et al., 1995; Bell et al., 2005; Manes et al., 2005; Mameniskiene et al., 2006; Butler et al., 2007; Davidson et al., 2007; Butler et al., 2009; Wilkinson et al., under review) using a variety of tests. The Rey-Osterreith Complex Figure test was used in two, Graham Kendall Memory for Designs test in two, visual selective reminding test in two and also dot locations subtest from Children‟s Memory Scale and visual reproduction of designs subtest of WMS-III. Four found significant accelerated forgetting in patients (Mameniskiene et al., 2006; Butler et al., 2007; Butler et al., 2009; Wilkinson et al., under review)– mostly using Rey-Osterreith complex figure, one found a trend towards accelerated forgetting (Davidson et al., 2007) and three found no evidence.

Thus, accelerated forgetting has been demonstrated in both verbal and non-verbal recall, with more evidence in verbal recall, across both story and word list testing. So it would seem to follow that testing for ALF would need to look at both verbal and non-verbal recall, as there is no strong evidence for one being more affected

than the other. Which is more affected is likely to be predicted by the laterality of the epilepsy as well, for example verbal memory would be more affected by epileptic foci in the left temporal lobe, as demonstrated by Blake et al (Blake et al., 2000).

The length of time delay used in the studies varies from 24 hours to eight weeks. In general, verbal accelerated forgetting seems to be more apparent earlier, from 24 hours (Martin et al., 1991), apart from in Bell‟s studies where it is not present at all. Non-verbal accelerated forgetting seems to be slightly more delayed, eg in Butler‟s study with one and three week test points, a trend for ALF is shown in non-verbal recall after one week and significant levels after three weeks, whereas significant ALF is shown in verbal recall after one week (Butler et al., 2007). Davidson et al, testing after one week, also only showed a trend towards ALF in non-verbal recall compared to significant ALF in verbal recall (Davidson et al., 2007). There are no studies testing over less than three weeks that demonstrate significant non-verbal ALF. Considering this, if non-verbal ALF is to be tested I would propose that the time delay would need to be at least three weeks from initial testing to a final delayed recall test.

Looking at the populations of patients studied, it is clear that there is evidence for accelerated long term forgetting in TEA in particular. Patients with TLE or partial epilepsies more generally have also been examined with slightly more mixed results, four studies showing accelerated forgetting over delays from 24 hours to eight weeks and three studies (two of which study largely the same population) finding no evidence for ALF. There is also a suggestion that the phenomenon might occur in children with idiopathic generalised epilepsy. Mameniskiene‟s study has also compared results within TLE patients between seizure types, finding those with simple partial seizures to have significantly less accelerated forgetting than those with complex partial and secondary generalised seizures during the study period (Mameniskiene et al., 2006)