known complexes have been reassembled, with the 
correct interaction consistently being at or near the 
top of the list. Fragments of known ligands can also 
be docked. Current work is aimed at incorporating 
recent advances in the calculation of interaction en- 
ergies and at developing the fragment-matching al- 
gorithms. As energy calculations improve and com- 
puters become faster and cheaper, this method 
should become a valuable drug design tool. 
Dr. Read is Associate Professor of Medical Micro- 
biology and Infectious Diseases and of Biochemis- 
try at the University of Alberta, Edmonton. 
Article 
Stein, P.E., Boodhoo, A., Tyrrell, G.J., Brunton, J.L., 
and Read, R.J. 1992. Crystal structure of the cell- 
binding B oligomer of verotoxin-1 from E. coli. 
Nature 355:748-750. 
REPRESENTATION OF TACTILE SIGNALS IN THE SOMATIC SENSORY CORTEX 
RanulfoRomo, M.D., Ph.D., International Research Scholar 
The somatic sensory system of subhuman pri- 
mates seems an appropriate model for approaching 
the question of how tactile signals are represented 
in the cerebral cortex. The hands of these animals 
and their brain structures related to somatic sensibil- 
ity are similar to those of humans. Similar sensory 
performance in somatesthetic tasks has also been 
observed in both primates. Moreover, the explor- 
atory movements of the hands have similar charac- 
teristics, since the somatic and motor systems in 
both cases are anatomically linked. 
Dr. Romo's laboratory is involved in studying the 
representation of tactile signals in the cerebral cor- 
tex and the mechanisms by which these signals are 
processed by the motor centers to guide motor be- 
havior. A first objective in this part of the research 
program is to define quantitatively the neural repre- 
sentation of moving tactile signals in areas 3b and 1 
of the primary somatic sensory cortex. The study 
consists of recording single neurons of areas 3b and 
1 with receptive fields in the primate's hand. These 
receptive fields are scanned with a probe in differ- 
ent directions and at variable speeds, at fixed tra- 
verse distance and constant force. With these data, 
Dr. Romo and his colleagues have defined the speed 
encoded by each neuron and the direction of the 
moving tactile stimulus. 
A Tactile Stimulator for Studying Motion 
Processing in the Somatic Sensory 
System of Primates 
It is well known that neurons in areas 3b and 1 of 
the somatic sensory cortex possess properties and 
receptive fields similar to those found in cutaneous 
primary afferents. However, the dynamic responses 
of these neurons to tactile stimuli are poorly under- 
stood. A difficulty encountered in somatosensory re- 
search has been the control of the presentation of 
stimulus parameters. For this purpose. Dr. Romo's 
laboratory has built a tactile stimulator for auto- 
matic presentation of very well controlled, moving 
stimuli in the receptive fields of the recorded neu- 
ron. This apparatus is used to assess the responses of 
neurons of the somatic sensory system to stimuli 
moving in any traverse distance (range, 2-20 mm), 
with a variety of velocities (range, 4-120 mm/s) 
and forces (range 0-60 gf), and in any scanning di- 
rection. The stimulator is highly automated and is 
currently used in human psychophysics and in com- 
bined psychophysical and neurophysiological stud- 
ies in behaving monkeys. 
Responses of Single Neurons of Areas 3b 
and 1 to the Speed of the Moving 
Tactile Stimulus 
Dr. Romo and his colleagues have studied quanti- 
tatively 178 neurons in five hemispheres of three 
awake Macaca mulattas. Ninety-six of these neu- 
rons were located in area 1 , and 82 in area 3b, all 
anatomically identified. According to their submo- 
dality (defined by their temporal adaptation to a 
steady, light mechanical stimulus applied to their 
receptive field) , 88 were classified as rapidly adapt- 
ing (RA; 61 in area 1, and 27 in area 3b), 61 as 
slowly adapting (SA; 19 in area 1, and 42 in area 
3b), 3 as pacinian (PC; all recorded in area 1), and 
26 as presenting RA SA properties (13 in area 1 and 
the same number in area 3b) . 
The distribution of submodalities encountered in 
this study agrees with that in the literature. The fir- 
ing rate of 129 neurons (72%) of the 178 studied 
responded at velocities from 20 to 100 mm/s. 
Groups of neurons of areas 3b and 1 were tuned to 
low (20 mm/s), intermediate (50 mm/s), or high 
INTERNATIONAL RESEARCH SCHOLARS 529 
