Graeme Whelan <gwhelan at access.net.au> wrote:
> I was interested to read that logical reasoning is not impaired by sleep
> loss....
This abstract by Jim Horne tells the main things, and he gives
references. I scanned the whole page from Sleep Res. Sorry for the
misprints, which are from my OCR program. I am in a hurry, so no more
now.
Dag Stenberg
Sleep Researcb Online 1999; 2 (Supplement 1) 677
FRONTAL LOBE FUNCTION AND SLEEP LOSS
Jim Horne
Loughborough University, UK
Most of the large number of studies undertaken into the effects of tota
sIeep deprivation (SD) on behaviour and psychologicai performance have
concentrated on measures deemed sensitive to "sleepiness", favouring
more basic low leve skills such as vigilance, reaction time, and aspects
of memory (1). These tests are usually combined with monotony and lack
of environmental stimulation, which together produce optimum conditions
for maximising the adverse eftects of SD. Such monotony is further
facilitated by the need to ensure that participants are welI trained in
the test proeedures beforehand, to minimise practice effects In
oontrast, the prevailing view in SD research is that high level, complex
skills are relatively unaffected by SD because of the interest they
generate and the implicit encouragement for participants to apply
compensatory effort to overcome their sieepiness. But it 5 still not
dear whether tasks associated with cognitive speed, psychomotor skiiis,
and visual and auditory attention, are so sensitive to one night of SD
other than by virtue of their monotony and Iack ot novelty, rather than
due to the more specific charactenstics of these tests. Wilkinson (2)
cautioned against using tasks that are ".. too complex, too interesting,
too variable and, above ali, too short" (pp 254256). He and many other
investigators have shown that these latter tasks (e.g. Iogical, concrete
reasoning) intrinsically encourage sleepy people to apply compensatory
eftort and perform normally. Hence, these tasks have been deemed to be
insensitive to SD. Similarly, with the dull, monotonous reaction time
and vigilance tasks, if participants are suitably encouraged to apply
more eftort, then performance retums to normal.
The most metabolically active region of the cortex during wakefulness is
the prefrontal cortex (PFC). inasmuch that: i ) the PFC seems to work
the hardest, and ii) that sleep may provide some form of recovery
process for the cortex, then one could argue that SD would particularly
affect the PFC. Recent findings (3) show that the PFC has the greatest
fali in regional waking cerebral metabolic rate following one night of
sleep Ioss. The PFC is largely not involved in any of the tasks
described above. Instead, it directs, sustains and focuses attention to
the task in hand by disregarding competing distraction and is the
"executive" co-ordinator of many oortical events. In particular, it
deals with novelty and the unexpected. Inasmuch that with practice and
training most comptex tasks lose their novelty and become more routine,
then in these respects they become less dependent on the PFC. The PFC is
responsible for "divergent", innovative and flexible thinking, as welI
as tempora memory. Neuropsychological tasks oriented to the PFC show
significant impairments with short-term SD (4-8). Such tests are short
and stimulating, and in these respects might not be expected to be
sensitive to sleep Ioss. But this is not the case. For example a
nonverbal task measuring flexibility in planning, which in healthy
participants causes signiflcant Ieft-prefrontal activation (9), is
significantly impaired by one night of SD (10). Language skills showing
impairment with SD, such as word fluency and word inhibition (5) rely
heavily on the integrity of the PFC (11). This same word fluency task
(5) Ieads to significant metabolic (PET) changes to the PFC following
36h of SD (12). Increased effort by the SD participant or the use of
psychostimulants to compensate for these PFC impairments are of only
iimited success (5,8). The PFC is not particulany associated with
logical or critical reasoning, especially if these tasks are familiar or
well-rehearsed. Such skills are not aftected by one night of SD (5,7).
Of course, it is possible that tests with a PFC orientation may simply
be more difficult than other tests without such a PFC focus, and that
our findings may not necessarily implicate the PFC, but simply task
"difficuIty". Nevertheless, these PFC findings have "real world"
implications for decision makers for example, working under emergency
oonditions and with little sleep - i.e. they wiIl experienoe
communication problems (impaired language skills), a Iack of innovation;
reduoed attention to peripheral ooncerns or distraction; over-relianoe
on previous strategies; unwillingness to try out novel strategies;
unreliable memory for when events occurred; change in mood including
Ioss of empathy with colleagues; and the inability to dea with surprise
and the unexpected.
1) Pitcher, JJ & Huffcutt, AI (1996) SIeep, 19: 318-326
2) Wilkinson, RT (1992) in: RJ Broughton,RD Ogilvie (Eds) SIeep,
Arousal and Performance. Boston, Birkhauser.
3) Thomas, M. et aI. (1993) J. Cereb.BIood FIow Metab.13 (suppl 1).
S351.
4) Harrison, Y & Horne JA (1997) SIeep, 20: 871-878
5) Harrison, Y & Horne JA (1998) J, SIeep Res. 7: 95-100.
6) Harrison Y & Horne JA (1998) J. SIeep Res. 7 (suppl 2), 113.
7) Harrison, Y & Horne JA (1999) Organis. Behav.Human Decision
Proc. (in press)
8) Harrison Y & Horne JA (1999) Quart. J. Exner. Psvchol. (in
press)
9) Morris, RG et al. (1993) NeuropsvchoIogia. 31, 1367-1378
10) Horne, J.A. (1988) SIeep, 11: 528-536
11) Frith, C et aI (1991) Proc. Royal Soc. Lond.B. 244: 241-246.
12) Petiau et al (1998) J. SIeep Res, 7. Suppl 2, 208.
< endit>
