In this study, we examined whether participation in a weekly group consisting of cognitive training and group psychotherapy has a beneficial effect on cognitive performance in PC patients and whether an improvement resulted from group participation or represented a temporal improvement effect during syndrome progression [23]. A total of 15 PC patients underwent an 8-week intervention, cognitive performance was assessed before and after intervention group participation. A control group of 15 PC patients underwent two cognitive testings with comparable time intervals without group intervention. Due to the exploratory nature of the study and to gain as much knowledge about cognitive impairment in PC as possible, 19 cognitive variables were considered. Due to the nonconfirmatory study design we decided to proceed without correction for multiple testing.

We observed significant improvements in the intervention group after invention group participation with moderate to large effects on a wide range of cognitive functions. There were significant improvements with a strong effect in attention and concentration performance measures. Memory measures showed a significant increase with medium to strong effects in working memory, verbal short-term memory and verbal and figural memory with delayed recall. No significant increase was observed in numerical short-term memory. The study yielded heterogeneous results regarding visuo-spatial skills, indicating a significant enhancement in visuo-spatial construction skills, but no statistically significant improvement in visuo-spatial analysis capability. Speech ability did not improve significantly for either semantic fluency or naming ability. Executive functions and processing speed did not show a significant increase in visuomotor speed but both visual screening ability and cognitive flexibility increased significantly. Thus it must be stressed, that due to the quasi-experimental design of the study, we cannot assume causality regarding the above stated results in the group intervention.

To analyze whether increases in cognitive performance could plausible be attributed to the effects of the group intervention, the performances of group participants were compared to a control group. Only three of 19 variables showed a significant interaction effect of time of testing and group membership. An interaction effect was present for verbal memory for the story: For both story learning and active delayed recall of the story, there was a significant interaction of time and group with a medium effect. In both variables the performance of the intervention group before group participation was below the performance of the control group, but after group participation it was above the performance of the control group. Thus, these increases cannot be attributed to time alone, but could also be related to effects of the group intervention. Due to the quasi-experimental design, no causal relation can be assumed. The same effect was seen in the visuospatial construction skills, where a significant interaction effect of time and group membership with a large effect was apparent. Performance of the intervention group was higher than performance of the control group in the second testing. Therefore the measured improvement is likely to not be the effect by time alone. Still, our results do indicate temporal effects in the direction of spontaneous recovery as well.

However, there was no significant interaction effect in the other 16 variables. Thus, the significant increases in the intervention group in the areas attention and concentration, working memory, verbal short-term memory and verbal delayed recall for the word list, figural memory, executive functions and processing speed cannot be explained by group participation alone but could also represent an improvement in PC symptomatology over time. Interestingly, a significant main effect of time was found for a large part of the variables, namely for attention and concentration performance for all three variables (concentration capacity, speed of operation and accuracy); for memory performance for 6 of the 9 variables (working memory, verbal short-term memory and delayed recall for the word list and figural memory); and for executive functions and processing speed for all three variables (visuomotor speed, visual screening ability and cognitive flexibility). Thus, for these 12 variables, regardless of whether patients participated in the intervention group or in the control group, there was an improvement in cognitive symptomatology over the average 113.87 days (intervention) and 121.53 days (control). This suggests that PC symptoms alleviate over time for a variety of cognitive complaints. There has been limited research on this [4], but initial studies also suggest that a natural improvement in cognitive complaints is possible over the course of PC [16]. Besides, in the second exploratory interview before testing, many patients stated that their complaints had subjectively improved over the course of the last few weeks.

This is not to say that cognitive training and group psychotherapy may not be helpful for PC patients. The limited research available on the effects of cognitive training and psychotherapy specifically targeting cognitive complaints in PC warrants further investigation before potentially dismissing this approach. The causal relation between cognitive training, time and PC symptoms remains elusive. Intervention group participation was also associated positively with a decrease in depressive symptoms showing a significant decrease in depressive symptomatology measured in the BDI-II [25]. Still, due to the study design depressiveness was only assessed in the intervention group. Therefore the evidence is limited, but indicates a promising trend. Regarding the feasibility of the intervention, most participants indicated that they found the group intervention helpful and relevant and were able to implement what was discussed in their daily lives. Many patients reported not knowing others affected by PC, found the exchange helpful and were relieved not to be left alone with their symptoms. Psychoeducation revealed how many were unaware of how common PC is and who they could turn to with their concerns. Nevertheless, there is still potential to optimize our intervention as many patients found the journey to the therapy sessions and the duration of the therapy sessions exhausting. Further, we did not find evidence indicating harmful effects of cognitive training in PC or a worsening of symptoms.

In the follow-up study, we will therefore try a video-based setting with shorter sessions. Moreover, it was noticeable, that many potential participants had expressed interest in the group therapy, but relatively few actually took part. This could be explained by the following aspects: overlapping rehab and other treatment measures, intermediate improvement of the symptomatology, too long travel times, too low energy level for the way and the duration of the session, overstrain due to too many other appointments, not compatible with the job. As stated above, an alternative approach could potentially be remote cognitive training and group psychotherapy from home.

In addition to the improvement over time, another explanation for the partial contradiction of Hypothesis 2 could be the selected test battery. It was chosen because it covers the possible cognitive complaints as broadly as possible; however, it may not be ideal for mapping PC relevant cognitive complaints. For example, many patients stated word-finding difficulties in everyday life which were rarely reflected in the semantic fluency subtest. Further research is needed to explore how PC-related cognitive complaints and improvements can be objectively represented. Subjective measures of cognitive performance might be useful as well: Frequently, perceived severe impairment was not reflected in objective tests, which, due to missing premorbid values, cannot provide information on how cognitive performance has deteriorated. Further, little is known about the gap between perceived and objective cognitive complaints in PC. Subjective measures might be more likely to represent improvement in symptomology after an intervention and to be closer to the patient’s perception.

In numerical short-term memory, visuo-spatial analysis ability, semantic fluency, and naming ability, there was no significant improvement in the intervention group, nor a significant main effect of time due to better performance on the second testing. Those findings suggest that within these domains, group participation did not have a significant impact and performance might not improve naturally over time during PC progression. These findings may however be explained by weaknesses in the design of neurocognitive assessments. PC-related impairments may be better reflected by other tests and by means of those, improvement over time should be re-assessed.

Patients were not randomly assigned to a group due to ethical issues and motivational aspects of the participants. Due to the exploratory character of the study there was no matching for age and gender. The study was conducted in a clinical healthcare context. Patients, who wished to participate in the intervention and were eligible were included in the intervention group. Many factors could not be controlled for in advance and due to the quasi-experimental study design. Thus, we cannot implicate a causality of the shown results. Further this bares the risk of a selection bias, which could have a systematic influence of the group differences. Additionally, no power analysis was conducted, and the raters were not blinded for the cognitive assessment. Due to the limited availability of trained personnel, there was a delay between the follow-up assessment and the final therapy session.

In future studies, an experimental design with longer treatment periods, randomized groups and larger sample sizes is needed to examine the effects of group intervention. Future research should control how long patients have been suffering from PC, as it can be assumed that symptoms may change over time and decrease nonlinearly. Furthermore information on the clinical presentation of the PC and comorbidities of the patients are needed. Additionally, cognitive performance in intervention and control group should controlled for at the baseline measurement. A third group, using a non-specific group intervention as therapy control group, could be useful. For all variables examined here, performance of the control group at the baseline measurement was higher than performance of the intervention group. Speed of operation and semantic fluency showed a main effect for the group intervention, performance of the control group was significantly higher on both assessments. In future studies with confirmatory design, fewer cognitive variables, like concentration and memory variables, should be assessed and corrected for multiple testing if necessary.