As shown in Fig. 1, a total of 1063 papers were identified, including 322 duplicates. After analyzing titles and abstracts, the studies not meeting the inclusion criteria were excluded. A total of 47 studies were considered.
The selected studies had different characteristics (see Table 2). The studies involved different populations and interventions: 30 studies involved healthy people (12–41), 9 studies involved people with MCI (42–50) and 3 studies involved people with mild to moderate dementia (51–53). In a few studies, samples were mixed, healthy people and people with MCI (54), healthy people and people with dementia (55–56), people with MCI or dementia (57–58).
Table 2
in the table are reported the following variables: author of the study, moments of valuation, length of primary intervention, presence of booster sessions, typology of training (single or multi-domain), cognitive functions trained, effect of the training in the follow-up (direct effect or far transfer effect) and for how many months or years the effect is maintained after the end of the training.
AUTHOR
|
POPULATION
|
VALUATION
|
PRIMARY INTERVENTION
|
BOOSTER SESSION
|
SINGLE OR
|
COGNITIVE FUNCTION
|
DIRECT EFFECT OR
|
DURATION OF EFFECTS
|
|
|
|
|
|
MULTI DOMAIN
|
|
FAR TRANSFER EFFECT
|
|
12
|
healthy people
|
1) baseline
|
12 sessions for
|
8 sessions
|
multi-domain
|
memory
|
after booster sessions:
|
3 months
|
|
|
2) PT
|
30 minutes
|
of 50 minutes
|
|
executive function
|
direct effect
|
after booster sessions
|
|
|
3) 3 years PT
|
(once a week)
|
twice a week
|
|
speed of processing
|
|
|
|
|
4) after booster sessions
|
|
|
|
|
|
|
|
|
5) 3 month after booster sessions
|
|
|
|
|
|
|
13
|
healthy people
|
1) baseline
|
10 sessions
|
X
|
multi-domain
|
memory
|
far transfer effect
|
3 months
|
|
|
2) PT
|
of 45 minutes
|
|
|
attention
|
|
|
|
|
3) 3 months PT
|
|
|
|
executive function
|
|
|
14
|
|
|
|
|
|
|
|
|
1° study
|
healthy people
|
1) baseline
|
3 sessions
|
X
|
single-domain
|
executive function
|
direct effect
|
6 months
|
|
|
2) PT
|
of 30/40 minutes
|
|
|
|
|
|
|
|
3) 6 months PT
|
in 3 forys
|
|
|
|
|
|
2° study
|
healthy people
|
1) baseline
|
6 sessions
|
X
|
single-domain
|
executive function
|
direct effect
|
6 months
|
|
|
2) PT
|
of 30/40 minutes
|
|
|
|
|
|
|
|
3) 6 months PT
|
in 2 weeks
|
|
|
|
|
|
15
|
healthy people
|
1) baseline
|
5 sessions
|
X
|
multi-domain
|
memory
|
far transfer effect
|
1 year
|
|
|
2) PT
|
of 120 minutes
|
|
|
attention
|
|
|
|
|
3) 6 months PT
|
(1 session every
|
|
|
executive function
|
|
|
|
|
4) 1 year PT
|
2 weeks)
|
|
|
visuospatial
|
|
|
|
|
|
|
|
|
skills
|
|
|
16
|
healthy people
|
1) baseline
|
15 sessions
|
X
|
single-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 20 minutes
|
|
|
|
|
|
|
|
3) 3 months PT
|
(3 sessions
|
|
|
|
|
|
|
|
|
for 5 weeks)
|
|
|
|
|
|
17
|
healthy people
|
1) baseline
|
14 sessions
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
|
2) PT
|
of 90 minutes
|
|
|
attention
|
|
|
|
|
3) 1 year PT
|
(2 sessions
|
|
|
executive function
|
|
|
|
|
|
for 7 weeks)
|
|
|
|
|
|
18
|
healthy people
|
1) baseline
|
24 sessions
|
X
|
single-domain
|
ragionamento
|
single-domain:
|
1 year
|
|
|
2) 1 year PT
|
of 1 hour
|
|
multi-domain
|
memory
|
direct effect
|
|
|
|
|
(2 sessions for
|
|
|
executive function
|
|
|
|
|
|
12 weeks)
|
|
|
visuospatial
|
multi-domain:
|
1 year
|
|
|
|
|
|
|
skills
|
far transfer effect
|
|
19
|
healthy people
|
1) baseline
|
15 sessions
|
X
|
single-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 45 minutes
|
|
|
|
|
|
|
|
3) 18 months PT
|
(3 sessions
|
|
|
|
|
|
|
|
|
for 5 weeks)
|
|
|
|
|
|
20
|
healthy people
|
1) baseline
|
27 sessions
|
1 booster session
|
multi-domain
|
memory
|
/
|
/
|
|
|
2) PT
|
of 40 minutes
|
per month
|
|
attention
|
|
|
|
|
3) after last booster
|
(3 sessions
|
of
|
|
executive function
|
|
|
|
|
session
|
for 8 weeks)
|
40 minutes
|
|
|
|
|
|
|
|
|
(for 3 months)
|
|
|
|
|
21
|
healthy people
|
1) baseline
|
12 sessions
|
X
|
single-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 45 minutes
|
|
|
|
|
|
|
|
3) 3 months PT
|
(3 sessions
|
|
single-domain
|
executive function
|
/
|
/
|
|
|
|
for 4 weeks)
|
|
|
|
|
|
22
|
healthy people
|
1) baseline
|
24 sessions
|
X
|
single-domain
|
executive function
|
direct effect
|
3 months
|
|
|
2) PT
|
of 30 minutes
|
|
|
|
|
|
|
|
3) 3 months PT
|
(3 sessions
|
|
|
|
|
|
|
|
4) 6 months PT
|
for 8 weeks)
|
|
|
|
|
|
23
|
healthy people
|
1) baseline
|
15 sessions
|
X
|
single-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 45/60
|
|
|
|
|
|
|
|
3) 1 year PT
|
minutes
|
|
|
|
|
|
|
|
|
(3 sessions
|
|
|
|
|
|
|
|
|
for 5 weeks)
|
|
|
|
|
|
24
|
healthy people
|
1) baseline
|
50 sessions
|
X
|
single-domain
|
executive function
|
direct effect
|
6 months
|
|
|
2) PT
|
of 45/60
|
|
single-domain
|
visuospatial skills
|
direct effect
|
6 months
|
|
|
3) 6 months PT
|
minutes
|
|
single-domain
|
visuospatial skills
|
/
|
/
|
|
|
|
(5 session for
|
|
|
|
|
|
|
|
|
10 weeks)
|
|
multi-domain
|
executive function
|
far transfer effect
|
6 months
|
|
|
|
|
|
|
visuospatial skills
|
|
|
25
|
healthy people
|
1) baseline
|
50 sessions
|
X
|
single-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 1 hour
|
|
|
|
|
|
|
|
3) 3 months PT
|
(5 sessions
|
|
|
|
|
|
|
|
|
for 10 weeks)
|
|
|
|
|
|
26
|
healthy people
|
1) baseline
|
12 sessions
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
|
2) PT
|
of 90 minutes
|
|
|
attention
|
|
|
|
|
3) 1 year PT
|
(2 sessions
|
|
|
executive function
|
|
|
|
|
|
for 6 weeks)
|
|
|
|
|
|
27
|
healthy people
|
1) baseline
|
24 sessions
|
X
|
multi-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 1 hour
|
|
|
memory
|
|
|
|
|
3) 5 years PT
|
(2 sessions
|
|
|
|
|
|
|
|
|
for 12 weeks)
|
|
|
|
|
|
28
|
healthy people
|
1) baseline
|
10 sessions
|
4 sessions
|
single-domain
|
executive function
|
/
|
/
|
|
|
2) PT
|
of 60/75
|
of 75 minutes
|
single-domain
|
memory
|
/
|
/
|
|
|
3) 1 year PT
|
minutes
|
at month 11
|
single-domain
|
speed of processing
|
before booster sessions:
|
|
|
|
4) 2 years PT
|
in 5/6 weeks
|
and at month 35
|
|
|
risk reduction
|
10 years
|
|
|
5) 3 years PT
|
|
after
|
|
|
after booster sessions:
|
|
|
|
6) 5 years PT
|
|
the primary intervention
|
|
|
risk reduction
|
7 years
|
|
|
7) 10 years PT
|
|
|
|
|
|
after booster sessions
|
29
|
healthy people
|
1) baseline
|
24 sessions
|
X
|
multi-domain
|
attention
|
direct effect
|
6 months
|
|
|
2) PT
|
of 1 hour
|
|
|
memory
|
|
|
|
|
3) 6 months PT
|
(2 sessions
|
|
|
|
|
|
|
|
|
for 12 weeks)
|
|
|
|
|
|
30
|
healthy people
|
1) baseline
|
10 sessions
|
X
|
single-domain
|
speed of processing
|
direct effect
|
2 years
|
|
|
2) PT
|
of 1 hour
|
|
|
|
|
|
|
|
3) 1 year PT
|
|
|
|
|
|
|
|
|
4) 2 years PT
|
|
|
|
|
|
|
31
|
healthy people
|
1) baseline
|
10 hours of
|
4 hours of training
|
single-domain
|
speed of processing
|
/
|
/
|
|
|
2) 1 years after
|
training in
|
at month 5 and at
|
|
|
|
|
|
|
baseline
|
5–6 weeks
|
month 11
|
|
|
|
|
|
|
|
|
after the primary
|
|
|
|
|
|
|
|
|
intervention
|
|
|
|
|
32
|
healthy people
|
1) baseline
|
60 sessions
|
X
|
multi-domain
|
attention
|
direct effect
|
3 months
|
|
|
2) PT
|
of 1 hour
|
|
|
speed of processing
|
|
|
|
|
3) 3 months PT
|
(in 3 months)
|
|
|
|
|
|
33
|
healthy people
|
1) baseline
|
24 sessions
|
1 session of
|
single-domain
|
executive function
|
before booster sessions:
|
|
|
|
2) PT
|
of 1 hour
|
1 hour, every
|
|
|
far transfer effect
|
1 year
|
|
|
3) 6 months PT
|
(2 sessions
|
month for 3 months
|
|
|
after booster sessions:
|
|
|
|
4) 1 year PT
|
for 12 weeks)
|
(after 6 months
|
multi-domain
|
memory
|
far transfer effect
|
6 months after boosters
|
|
|
|
|
from the
|
|
executive function
|
before booster sessions:
|
|
|
|
|
|
primary intervention)
|
|
|
far transfer effect
|
1 year
|
|
|
|
|
|
|
|
after booster sessions:
|
|
|
|
|
|
|
|
|
far transfer effect
|
6 months after boosters
|
34
|
healthy people
|
1) baseline
|
36 sessions
|
24 sessions
|
single-domain
|
memory
|
after booster sessions:
|
immediatly after
|
|
|
2) PT
|
for 30 minutes
|
for 30 minutes
|
|
|
far transfer effect
|
booster sessions
|
|
|
3) 3 months PT
|
(in 3 months)
|
(in 3 months)
|
|
|
|
|
|
|
|
|
in the 3 months
|
|
|
|
|
|
|
|
|
after the
|
|
|
|
|
|
|
|
|
primary intervention
|
|
|
|
|
35
|
healthy people
|
1) baseline
|
12 sessions
|
X
|
single-domain
|
multitasking capacity
|
direct effect
|
6 months
|
|
|
2) PT
|
for 1 hour
|
|
|
|
|
|
|
|
3) 6 months PT
|
(3 sessions
|
|
|
|
|
|
|
|
|
for 4 weeks)
|
|
|
|
|
|
36
|
healthy people
|
1) baseline
|
60 minutes
|
X
|
multi-domain
|
memory
|
direct effect
|
3 months
|
|
|
2) PT
|
per day
|
|
|
executive function
|
|
|
|
|
3) 3 months PT
|
for 5 times at week
|
|
|
speed of processing
|
|
|
|
|
|
(for 8/10 weeks)
|
|
|
|
|
|
37
|
healthy people
|
1) baseline
|
10 sessions
|
4 sessions
|
single-domain
|
executive function
|
before booster sessions:
|
|
|
|
2) PT
|
for 60/75
|
for 75 minutes
|
|
|
direct effect
|
10 years
|
|
|
3) 1 year PT
|
minutes
|
at month 11
|
|
|
after booster sessions:
|
|
|
|
4) 2 years PT
|
in 5/6 weeks
|
and at month 35
|
|
|
direct effect
|
7 years after boosters
|
|
|
5) 3 years PT
|
|
after the primary
|
single-domain
|
speed of processing
|
before booster sessions:
|
|
|
|
6) 5 years PT
|
|
intervention
|
|
|
direct effect
|
10 years
|
|
|
7) 10 years PT
|
|
|
|
|
after booster sessions:
|
|
|
|
|
|
|
|
|
direct effect
|
7 years after boosters
|
|
|
|
|
|
single-domain
|
memory
|
before booster sessions:
|
|
|
|
|
|
|
|
|
direct effect
|
5 years
|
|
|
|
|
|
|
|
after booster sessions:
|
|
|
|
|
|
|
|
|
/
|
/
|
38
|
healthy people
|
1) baseline
|
12 sessions
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
|
2) PT
|
for 90 minutes
|
|
|
attention
|
|
|
|
|
3) 9 months PT
|
(1 sessions
|
|
|
executive function
|
|
|
|
|
|
for 12 weeks)
|
|
|
|
|
|
39
|
healthy people
|
1) baseline
|
3 sessions for
|
X
|
single-domain
|
executive function
|
far transfer effect
|
8 months
|
|
|
2) PT
|
60 minutes
|
|
|
|
|
|
|
|
3) 8 months PT
|
(in 2 weeks)
|
|
|
|
|
|
40
|
healthy people
|
1) baseline
|
20 minutes
|
X
|
multi-domain
|
memory
|
direct effect
|
3 weeks
|
|
|
2) PT
|
every day for
|
|
|
executive function
|
|
|
|
|
3) 3 weeks PT
|
21 days
|
|
|
speed of processing
|
|
|
41
|
healthy people
|
1) baseline
|
every phase consists
|
every phase
|
multi-domain
|
executive function
|
/
|
/
|
|
|
phase 1
|
of
|
after the phase 1
|
|
attention
|
|
|
|
|
2) after phase 1
|
20 sessions
|
is considered a
|
|
language
|
|
|
|
|
3) 1 year after
|
for 50 minutes
|
booster session
|
|
memory
|
|
|
|
|
the end of phase 1
|
(2 sessions
|
|
|
|
|
|
|
|
phase 2
|
for 12 weeks)
|
|
|
|
|
|
|
|
4) after the phase 2
|
|
|
|
|
|
|
|
|
5) 1 year after
|
80 total sessions
|
|
|
|
|
|
|
|
phase 2
|
|
|
|
|
|
|
|
|
phase 3
|
|
|
|
|
|
|
|
|
6) after phase 3
|
|
|
|
|
|
|
|
|
7) 1 year after
|
|
|
|
|
|
|
|
|
phase 3
|
|
|
|
|
|
|
|
|
phase 4
|
|
|
|
|
|
|
|
|
8) after phase 4
|
|
|
|
|
|
|
42
|
MCI
|
1) baseline
|
120/160 minutes
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
|
2) PT
|
of training
|
|
|
executive function
|
|
|
|
|
3) 1 year PT
|
every week
|
|
|
visuospatial skills
|
|
|
|
|
|
(for 6 months)
|
|
|
|
|
|
43
|
MCI
|
1) baseline
|
30 minutes
|
X
|
multi-domain
|
executive function
|
far transfer effect
|
3 months
|
|
|
2) PT
|
every day for
|
|
|
attention
|
|
|
|
|
3) 3 months PT
|
12 weeks
|
|
|
language
|
|
|
|
|
|
|
|
|
visuospatial skills
|
|
|
44
|
MCI
|
1) baseline
|
8 sessions for
|
1 session
|
multi-domain
|
memory
|
before booster sessions:
|
|
|
|
2) PT
|
120 minutes
|
for 120 minutes
|
|
attention
|
direct effect
|
3 months
|
|
|
3) 3 months PT
|
|
after 3 months after
|
|
|
after booster sessions:
|
|
|
|
4) 6 months PT
|
|
the end of the primary
|
|
|
direct effect
|
3 months
|
|
|
|
|
intervention
|
|
|
|
|
45
|
MCI
|
1) baseline
|
12 hours of training
|
4 sessions for
|
single-domain
|
memory
|
after booster sessions:
|
20 months
|
|
|
2) PT
|
|
2 hours
|
|
|
direct effect
|
after booster sessions
|
|
|
3) 4 months PT
|
|
(once a week
|
|
|
|
|
|
|
5) 1 year PT
|
(2 sessions
|
3 months after the end
|
|
|
|
|
|
|
6) 2 years PT
|
for 6 weeks)
|
of primary intervention)
|
|
|
|
|
46
|
MCI
|
1) baseline
|
48 sessions for
|
X
|
multi-domain
|
memory
|
far transfer effect
|
6 months
|
|
|
2) 12 months after baseline
|
120 minutes
|
|
|
attention
|
|
|
|
|
|
(2 sessions
|
|
|
speed of processing
|
|
|
|
|
|
for 24 weeks)
|
|
|
|
|
|
47
|
MCI
|
1) baseline
|
24 sessions
|
X
|
multi-domain
|
memory
|
direct effect
|
6 months
|
|
|
2) PT
|
for 1 hour
|
|
|
executive function
|
|
|
|
|
3) 6 months PT
|
(2 sessions
|
|
|
attention
|
|
|
|
|
|
for 12 weeks)
|
|
|
|
|
|
48
|
MCI
|
1) baseline
|
5 sessions for
|
X
|
single-domain
|
memory
|
direct effect
|
4 months
|
|
|
2) 2 weeks PT
|
90 minutes
|
|
|
|
|
|
|
|
3) 4 months PT
|
(1 session for
|
|
|
|
|
|
|
|
|
5 weeks)
|
|
|
|
|
|
49
|
MCI
|
1) baseline
|
10 sessions for
|
2 booster session:
|
multi-domain
|
memory
|
before booster sessions:
|
|
|
|
2) 5 weeks PT
|
90 minutes
|
the first booster
|
|
attention
|
far transfer effect
|
1 month
|
|
|
3) 1 year PT
|
in 5 weeks
|
after 6 months
|
|
executive function
|
after booster sessions:
|
|
|
|
4) 2 years PT
|
|
after the baseline valutation
|
|
speed of processing
|
direct effect
|
1 year after booster
|
|
|
|
|
the second booster
|
|
language
|
|
|
|
|
|
|
after 1 year follow-up
|
|
|
|
|
|
|
|
|
valuation
|
|
|
|
|
50
|
MCI
|
1) baseline
|
25 sessions for
|
X
|
single-domain
|
executive function
|
direct effect
|
3 months
|
|
|
2) PT
|
40 minutes
|
|
single-domain
|
executive function
|
direct effect
|
3 months
|
|
|
3) 3 months PT
|
(in 5–7 weeks)
|
|
|
|
|
|
51
|
mild dementia
|
1) baseline
|
first training:
|
2 training
|
single-domain
|
executive function
|
before booster sessions:
|
|
|
|
2) after the first
|
6 sessions for 30
|
separated
|
|
|
far transfer effect
|
1 month
|
|
|
training
|
minutes
|
from 1 month of break
|
|
|
|
|
|
|
3) after
|
(1 session for
|
for this the second
|
|
|
after booster sessions:
|
|
|
|
1 month
|
6 weeks)
|
training is
|
|
|
far trasnfer effect
|
3 months after booster
|
|
|
4) after the end of the
|
|
considered a booster of
|
|
|
|
|
|
|
second training
|
second training:
|
the first
|
|
|
|
|
|
|
5) after 1 month after
|
6 sessions for 30
|
|
|
|
|
|
|
|
the second training
|
minutes
|
|
|
|
|
|
|
|
6) 3 months after
|
(1 session for
|
|
|
|
|
|
|
|
the second training
|
6 weeks)
|
|
|
|
|
|
52
|
dementia: from mild to
|
1) baseline
|
24 sessions
|
extra training
|
single-domain
|
executive function
|
before boosters
|
/
|
|
moderate
|
2) PT
|
for 45 minutes
|
|
|
|
after booster sessions:
|
/
|
|
|
3) 3 months PT
|
(2 sessions for
|
|
|
|
|
|
|
|
|
12 weeks)
|
|
|
|
|
|
53
|
dementia: from mild to
|
1) baseline
|
48 sessions
|
X
|
multi-domain
|
memory
|
direct effect
|
6 months
|
|
moderate
|
2) PT
|
for 75 minutes
|
|
|
attention
|
|
|
|
|
3) 6 months PT
|
(2 sessions for
|
|
|
executive function
|
|
|
|
|
|
24 weeks)
|
|
|
language
|
|
|
|
|
|
|
|
|
visuospatial skills
|
|
|
54
|
healthy people
|
1) baseline
|
25 sessions
|
X
|
single-domain
|
executive function
|
far transfer
|
3 months
|
|
MCI
|
2) PT
|
for 45 minutes
|
|
healthy people
|
|
|
|
|
|
3) 3 months PT
|
(5 sessions
|
|
|
|
|
|
|
|
|
for 5 weeks)
|
|
single-domain
|
executive function
|
direct effect
|
3 months
|
|
|
|
|
|
MCI
|
|
|
|
55
|
dementia: from mild to
|
1) baseline
|
3 times at week
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
moderate
|
2) PT
|
for
|
|
healthy people
|
activities
|
|
|
|
healthy people
|
3) 3 weeks PT
|
4 weeks
|
|
|
of daily life
|
|
|
|
|
|
|
|
multi-domain
|
memory
|
/
|
/
|
|
|
|
|
|
dementia
|
activities of
|
|
|
|
|
|
|
|
|
daily life
|
|
|
56
|
healthy people
|
1) baseline
|
12 sessions for
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
dementia
|
2) PT
|
45 minutes
|
|
healthy people
|
language
|
|
|
|
|
3) 2 months PT
|
(2 sessions
|
|
|
visuospatial skills
|
|
|
|
|
|
for 6 weeks)
|
|
|
executive function
|
|
|
|
|
|
|
|
|
attention
|
|
|
|
|
|
|
|
multi-domain
|
memory
|
far transfer effect
|
2 months
|
|
|
|
|
|
dementia
|
language
|
|
|
|
|
|
|
|
|
visuospatial skills
|
|
|
|
|
|
|
|
|
executive function
|
|
|
|
|
|
|
|
|
attention
|
|
|
57
|
mild dementia
|
1) baseline
|
30 sessions for
|
X
|
multi-domain
|
attention
|
far transfer effect
|
9 months
|
|
MCI
|
2) PT
|
1 ora
|
|
(paper and pencil
|
memory
|
|
|
|
|
3) 9 months PT
|
(2/3 sessions
|
|
training and
|
executive function
|
|
|
|
|
|
for 12 weeks)
|
|
computerized training)
|
language
|
|
|
|
|
|
|
|
multi-domain
|
attention
|
/
|
/
|
|
|
|
|
|
(paper and pencil
|
memory
|
|
|
|
|
|
|
|
training)
|
executive function
|
|
|
|
|
|
|
|
|
language
|
|
|
58
|
dementia
|
1) baseline
|
12 sessions for
|
X
|
multi-domain
|
memory
|
/
|
/
|
|
MCI
|
2) PT
|
1 hour
|
|
|
language
|
|
|
|
|
3) 3 months PT
|
(3 sessions for
|
|
|
attention
|
|
|
|
|
4) 9 months PT
|
4 weeks)
|
|
|
|
|
|
HEALTHY PEOPLE
Among the 33 studies involving healthy people (12–41, 54–56) (i.e., 30 works involved only healthy individuals and 3 works involved mixed samples), 7 compared the effectiveness of different cognitive trainings (14, 18, 21, 24, 28, 33, 37). For that, a total of 44 intervention groups were studied: 26 were single-domain training (14,16,18–19,21−25,28,30–31,33−35,37,39,54) and 18 were multi-domain training (12–13,15,17–18,20,24,26–27,29,32–33,36,38,40–41,55−56).
The effect of cognitive training before the use of booster sessions
The analysis of the intervention groups showed that 24 groups out of 44 improved their performance in the follow-up analyses, in comparison to the baseline assessment, before the use of booster sessions (13–15, 18, 22, 24, 28–30, 32–33, 35–37, 39–40, 54). Of these 24 groups, 15 groups received single-domain training (14, 18, 22, 24, 28, 30, 33, 35, 37, 39, 54) and 9 groups received multi-domain training (13, 15, 18, 24, 29, 32–33, 36, 40).
In the follow-up, 22 out of 24 groups maintained their performance in the follow-up analysis (13–14, 18, 22, 28–30, 32–33, 35–37, 39–40, 54); in 2 out of 24 groups, the performance increased further (15, 24). Generally, benefits lasted from 3 weeks to 10 years after the intervention. Specifically, 6 groups showed benefits between 3 weeks and 3 months (13, 22, 32, 36, 40, 54), while 7 groups demonstrated benefits during 6 months after training (14, 24, 29, 35). The group in the study of Borella et al. (39) showed positive intervention effects 8 months after the training, whereas 5 groups had benefits even 1 year after the training (15, 18, 33). At the same time, 5 groups showed persistent effects 2 years (30), 5 years (37) and 10 years (28, 37) after the training. In contrast, for the remaining 20 groups (12, 16–17, 19–21, 23–27, 31, 34, 38, 41, 55–56), the improvements achieved with the training were not maintained or further amplified in the follow-up analyses. However, the 20 groups showed a maintenance of initial performance prior to the training.
Single-domain cognitive training
Eleven of the 15 groups using single-domain training showed that this type of training had a direct effect (14, 18, 22, 24, 30, 35, 37). Five groups (14, 18, 22, 24) receiving a training focused on executive functions, lasting on average 17 hours over 5 weeks, improved their performance up to 1 year after the intervention. On the other hand, one group (24) indicated that exercising visual-spatial skills for 44 hours over 5 weeks improved them compared to baseline during the following 6 months. At the same time, Vance et al. (30) found that exercising the speed of processing for 10 hours improved this ability up to 2 years. Anguera et al. (35) also noted that receiving a training focused on multitasking capacity lasting 12 hours in one month, showed benefit during the following 6 months.
A particular case was represented by the ACTIVE study (37); 3 intervention groups had a direct effect. This work demonstrated that training speed of processing and executive functions, for 11 hours in 6 weeks, improved the trained domains for up to 10 years after training. Contemporary training memory for 11 hours in 6 weeks secured benefits for up to 5 years after the initial intervention.
In contrast, 3 groups (33, 39, 54) showed far transfer effects. Training executive functions for an average of 15 hours in 6 weeks led to an increase in memory, attention, language, visual-spatial skills, and speed of processing for up to 1 year after the initial intervention.
Finally, within the ACTIVE study, Edwards et al. (28) found a 29% risk reduction of developing dementia for up to 10 years after the intervention.
Multi-domain cognitive training
Four out of the 9 groups using multi-domain training (29, 32, 36, 40) had a direct effect. Indeed, 2 groups showed that exercising attention and memory (29), or attention and speed of processing (32), for an average of 42 hours over 3 months, led to improvements in memory (29), or speed of processing (32), for up to 6 months after training. In addition, 2 groups (36, 40) indicated that training mainly on speed of processing and executive functions, on average for 30 hours over 3 months, led to boosting speed of processing and executive functions from 3 weeks to 3 months after training.
The remaining 5 groups (13, 15, 18, 24, 33) showed that multi-domain training led to far transfer effects. Specifically, 2 groups (18, 33) enhanced attention and language ability 1 year after a training focused on memory and executive functions which lasted 24 hours for 3 months. Binder et al. (24) indicated an improvement in attention for up to 6 months after training visual-spatial skills and executive functions for 44 hours in 5 weeks. Kazazi et al. (13) showed an improvement in life quality 3 months after training attention and executive functions for 8 hours. Finally, Srisuwan et al. (15) demonstrated a reduction in anxiety 1 year after exercising attention, memory, executive functions, and visual-spatial skills for 10 hours distributed across 2 months.
The effect of cognitive training after the use of booster sessions
Booster sessions were delivered within 13 groups (12, 20, 28, 31, 33–34, 37, 41). Seven of them maintained and amplified benefits obtained with the initial training for up to 7 years (12, 28, 33–34, 37).
Single-domain training booster sessions
Five of 7 intervention groups showed improved performance after the booster sessions adopting a single domain training (28, 33–34, 37). Of these 5, 2 groups used the additional sessions targeting executive functions for 7 hours and noticed direct effects lasting from 3 months to 7 years after their use (33, 37). Further, Cheng et al. (33) showed that, by working on executive functions for 3 hours, the positive effect is also transferred to speed of processing, visual-spatial and constructive skills for up to 6 months later. Rebok et al. (37) demonstrated booster sessions’ direct effect on speed of processing when participants were trained for 10 hours, for up to 7 years after the sessions ended. Edwards et al. (28) noted that additional sessions focusing on speed of processing further reduced the risk of dementia over the following 7 years.
Regarding memory training booster sessions, while Rebok et al. (37) showed their ineffectiveness, Optale et al. (34) found that sessions, used for 18 hours, had a far transfer effect on executive functions, general cognitive functioning, and reduction of depressive symptoms.
Multi-domain training booster sessions
Multi-domain training booster sessions were reported to produce positive effects in 2 groups (12, 33). The sessions, which averaged 5 hours, primarily focused on memory and executive functions, which benefitted from the sessions for 3 to 6 months after their use.
Moreover, Cheng et al. (33) noted far transfer effect on speed of processing, visuospatial and constructive abilities within 6 months after the additional sessions.
PEOPLE WITH MCI
Among the 12 studies involving people with MCI (42–50, 54, 57–58) (i.e., 9 people with MCI and 3 mixed samples), some groups (50, 57) compared the effectiveness of two interventions applied to two different groups. Therefore, a total of 14 intervention groups were analyzed. Of these, 5 groups used single-domain training (45, 48, 50, 54), while 9 used multi-domain training (42–44, 46–47, 49, 57–58).
The effect of cognitive training before the use of booster sessions
Ten groups, including 4 single-domain training (48, 50, 54) and 6 multi-domain training (43–44, 46–47, 49, 57), demonstrated that cognitive training improved the performance of individuals with MCI. This was demonstrated by comparing baseline performance against performance in follow-up analysis, but before the use of booster sessions.
In the follow-up, 9 out of 10 groups maintained their performance in the follow-up analysis (43–44, 46–50, 54); in 1 out of 10 groups, the performance increased further (57).
Benefits were evident from 1 to 9 months after training. Specifically, 7 intervention groups demonstrated gains from 1 to 4 months (43–44, 48–50, 54). Moreover, 2 groups had positive results during the 6 months following the intervention (46–47). Only Gaitan et al. (57) found a significant effect 9 months after training.
The remaining 4 groups (42, 45, 57–58), on the other hand, showed that the training did not improve the subjects' performance, compared to baseline, in the follow-up analyses before the booster sessions. Nevertheless, one of these studies (58) suggested that the performance of individuals who underwent cognitive training, although not improving, was maintained up to 9 months after the intervention. This contrasted with the control group, who showed a decline in performance.
Single-domain cognitive training
The 4 groups who underwent single-domain training showed a direct effect (48, 50, 54). Three intervention groups (50, 54) exercised executive functions for an average of 18 hours over 5 weeks, improving them for up to 3 months after training. Kinsella et al. (48) showed that, when exercised for 8 hours over 5 weeks, memory enhanced for up to 4 months after the intervention.
Multi-domain cognitive training
Of the 6 groups using multi-domain training, 2 groups showed direct effects. As a matter of fact, Belleville et al. (44) noted an improvement in memory after exercising it, together with attention, for 16 hours in the following 3 months. On the other hand, Herrera et al. (47) showed an improvement in executive functions up to 6 months after training this ability, together with memory and attention, for 24 hours over 3 months.
In contrast, 4 studies indicated a far transfer effect to untrained domains. Rojas et al. (46) found that training memory, attention, and speed of processing for 96 hours over 6 months led to improvements in language and executive functions over the following 6 months. On the contrary, 2 intervention groups (43, 57) indicated that training various cognitive functions, such as attention, language, and executive functions, for an average of 36 hours in 3 months reduced depression 3 months after the intervention (43) and anxiety 9 months later (57). Finally, Vidovich et al. (49) showed that training memory, attention, language, speed of processing and executive functions for 15 hours in 5 weeks increased life’s quality 1 month after the training.
The effect of cognitive training after the use of booster sessions
As regards booster sessions, 3 out of 14 groups used and noticed session effectiveness for 3 up to 20 months after their use (44–45, 49).
Single-domain training booster sessions
McDougall et al. (45) demonstrated that additional sessions of single-domain memory-focused training practiced for 8 hours in 1-month improved memory in the following 20 months.
Multi-domain training booster sessions
Belleville et al. (44) and Vidovich et al. (49) indicated that multi-domain training’s booster sessions, used for 2 hours, enhanced memory for 3 months (44) and executive function for 1 year (49) after using the booster sessions.
PEOPLE WITH DEMENTIA
Seven studies involved people with dementia (51–53, 55–58) (i.e., 3 people with dementia and 4 mixed samples). Only Gaitan et al. (57) compared two different interventions. Thus, 8 intervention groups were analyzed, of which 2 used single-domain training (51–52) and 6 multi-domain training (53, 55–58).
The effect of cognitive training before the use of booster sessions
The intervention groups' analysis showed that 4 out of 8 improved their performance in the time after the end of the intervention, compared to the baseline assessment, before using booster sessions. One group was single-domain (51), and 3 groups were multi-domain (53, 56–57).
In the follow-up, 2 out of 4 groups maintained their performance in the follow-up analysis (53–56); in 2 out of 4 groups, the performance increased further (51, 57).
Generally, benefits persisted from 1 to 9 months after the intervention. Specifically, benefits were maintained for 1 month (51), 2 months (56), 6 months (53) and 9 months (57) after training.
In contrast, the remaining 4 groups (52, 55, 57–58) showed no improvements in the follow-up analyses compared to baseline. Galante et al. (58) indicated performance maintenance for the 9 months following the intervention. Meanwhile, the control group’s performance was declining.
Single-domain cognitive training
Only the study of Shyu et al. (51) demonstrated the effectiveness of single-domain training. The training focused on executive functions for 3 hours over 6 weeks. It showed a far transfer effect: improving quality of life and reducing depressive symptoms within 1 month after training.
Multi-domain cognitive training
Three studies used multi-domain training. Trebbastoni et al. (53) found a direct effect of the training. As a matter of fact, the study showed that training focused on attention, language, executive functions, and memory for 60 hours over 6 months led to just an improvement in memory. The effect was stable for up to 6 months. Ekcroth-Bucher et al. (56), on the other hand, indicated that exercising different cognitive domains, such as memory, language, and executive functions, for 9 hours in 6 weeks improved DRS scores up for 2 months after the interventions. Finally, Gaitan et al. (57) indicated that training focused on attention, language, and executive functions for 30 hours over 3 months reduced anxiety 9 months later.
The effect of cognitive training after the use of booster sessions
Regarding booster sessions, among the 8 intervention groups, only 2 groups used the booster sessions (51–52).
Single-domain training booster sessions
Shyu et al. (51) performed booster sessions of a single domain training for 3 hours over 6 weeks. The sessions focused on executive functions helped reducing depressive symptoms while increasing quality of life, even after 3 months. In contrast, Kallio et al. (52) indicated the lack of efficacy of cognitive training and booster sessions in people with dementia.