Materials and methods spheres at co-ordinates AP 17.0 to 18.0 mm [57]. The
36 C
ments in marmosets with ablations confined to the in- matched for learning ability on the basis of performance on
ferotemporal cortex [53]. Marmosets with lesions of the these tasks. Monkeys from the two sources named above
NBM1VDB or fornix transection alone show learning were distributed between the two new groups. Monkeys in
¨ impairments
but not
the Kluver–Bucy
syndrome Group C2 n54 were unoperated and monkeys in Group
¨ [47,48,50,52].
The occurrence
of the
Kluver–Bucy L2 n54 had the same surgical procedure as monkeys in
syndrome in marmosets with transection of the anterior Group L1.
temporal stem, amygdala and fornix would therefore be unlikely to be just a consequence of impaired visual
2.2. Surgery discrimination learning ability.
Some authors have considered the symptoms of the For surgery, each monkey was premedicated with 0.05
¨ Kluver–Bucy syndrome in macaques to be the behavioural
ml ketamine 100 mg ml, i.m., Vetalar, Pharmacia, Lux- manifestation of visual agnosia, i.e., a gross impairment of
embourg and anaesthetised with 18 mg kg alphaxolone– visual analysis [21,33]. Although macaques with small
alphadolone i.m., Saffan, Schering-Plough, Welwyn Gar- ¨
inferotemporal lesions do not exhibit florid Kluver–Bucy den City, UK. Dexamethasone 2 mg kg, i.m., Merck,
signs, it has been argued that their learning impairment Sharpe and Dohme, Harlow, UK was given just before
also arises from some sort of difficulty with visual analysis surgery, to limit cerebral oedema. Each monkey was
rather than from a memory impairment per se [18]. It is placed in a stereotaxic frame and, following incision of the
therefore pertinent to ask whether the behavioural dis- skin and retraction of the temporal muscles, a large cranial
turbance and or the learning impairment seen after trans- flap was removed to allow a clear view of the dorsal and
ection of the anterior temporal stem, amygdala, and fornix lateral surfaces of the brain. A large stellate incision was
could also be attributed to difficulties in visual analysis. made in the dura mater over the surface of one hemisphere
and the dural flaps retracted. A small hole was made by suction through the corpus callosum between the hemi-
2. Materials and methods spheres at co-ordinates AP 17.0 to 18.0 mm [57]. The
bifurcation of the fornix was identified and each arm of the 2.1. Animals
fornix was elevated and transected, either by using a hooked, 19-gauge hypodermic needle by RMR, or by
2.1.1. Experiment 1 direct suction ablation by DG.
Ten laboratory-born common marmosets Callithrix Immediately after the fornix transection had been made,
jacchus, six male and four female, were used in Experi- the temporal stem and amygdala was transected. A suction
ment 1. They were each aged about 12 months and incision was made in the left temporal lobe about 2 mm
weighed 300–350 g at the beginning of the experiment. below the lateral sulcus and angled down at about 458.
Before surgery, the monkeys were trained on a series of This steep approach was taken so that auditory cortex,
discrimination learning tasks see below and were as- rather then visual cortex, was compromised by the surgery.
signed to one of two groups matched for learning ability. The incision was continued until the floor of the cranium
Group C1 n55 were unoperated controls and Group L1 was encountered and the incision was extended rostrally to
n55 received bilateral fornix transection and a bilateral within 2 mm of the temporal pole and caudally to the
temporal lobe incision which transected the temporal stem beginning of the lateral ventricle adjacent to the anterior
and the amygdala. At the end of Experiment 1, the extremity of the hippocampus. This incision was intended
monkeys in Group L1 were perfused for histological brain to traverse the white matter of the superior temporal gyrus,
analysis. leaving the insula and temporal neocortex intact, and to
transect the temporal stem and amygdala. The lateral 2.1.2. Experiment 2
sulcus was left intact because this contains the middle In Experiment 2, five of the unoperated monkeys from
cerebral artery, damage to which could have produced a Group C1 of Experiment 1 together with five other
large cerebral infarction. The dura mater were closed using marmosets which were unoperated control monkeys from
6 0 vicryl sutures and the procedure was repeated in the another study [50] and which had a comparable degree of
right hemisphere. The cranial flap was replaced, the cognitive testing, were used to assess the effect of a
temporal muscles
reattached to
the skull
with cholinergic receptor agonist pilocarpine on the lesion-
cyanoacrylate glue Vetbond, Animal Care Products, Ger- induced cognitive impairment. One monkey was sub-
many, and the skin sewn with 3 0 vicryl sutures. sequently removed from the study because histological
analysis revealed that its lesion failed to comply with the 2.3. Cognitive testing
intended removal and another, unoperated monkey could not be assessed because it refused to perform trials under
All monkeys were trained to perform discrimination pilocarpine, leaving four animals in each group. The
tasks in a Wisconsin General Test Apparatus WGTA monkeys were first trained on a series of discrimination
using standard methods [4]. Approximately 40 trials were learning tasks and were then assigned to one of two groups
given to each monkey on each weekday and, in order to
C .J. Maclean et al. Brain Research 888 2001 34 –50
37
maintain motivation, the monkeys were fed their normal i.p., the monkeys were deeply anaesthetised with 1.0 ml
daily diet of bread, fruit and monkey pellets after testing sodium pentobarbitone 200 mg ml, i.p. and perfused
each day. Three types of task were used: coloured object transcardially with 250 ml ice-cold phosphate-buffered
Object discrimination either as single discriminations or saline PBS, pH 7.4, followed by 300 ml ice-cold 4
as 10 concurrent discriminations, black object Shape paraformaldehyde in 0.1 M phosphate buffer, pH 7.4. The
discrimination, and spatial discrimination. brains were removed and postfixed for 2 h in ice-cold 4
For Object discrimination, two small plastic coloured paraformaldehyde in phosphate buffer, after which they
junk objects were presented over two food-wells in the were inspected visually. Diagrammatic drawings were
WGTA and the monkey had to learn to displace the made of the cortical damage in monkeys in Groups L1 and
appropriate object to retrieve a small food reward usually L2 and the brains of monkeys in Group L2 were also
a piece of marshmallow. The left–right position of the photographed. The brains were then cut coronally into
two objects varied pseudorandomly but the reward was blocks that were transferred to 30 sucrose–PBS at 48C
always found under the same object. For Shape discrimina- for 2 to 3 days. The blocks were transferred to fresh 30
tion, two small junk objects painted black all over were sucrose–PBS after 24 h. Using a freezing stage microtome,
used as stimuli. These two tasks differ in the type of sections were cut throughout the brain. Sections 40 mm
perceptual analysis needed for task solution. While were stained for acetylcholinesterase AChE activity
coloured objects can be distinguished by overall appear- [34,51] or with Cresyl Violet.
ance or by identifying differences in individual features e.g., differently coloured parts, the black objects can only
be distinguished by perceiving differences in the shape of