the way they represent visual
information  or their particular
patterns of connectivity , may
be better than others in allowing
artiﬁcial activity to seep into
consciousness. Murphey and
Maunsell  addressed this
possibility by measuring thresholds
from ﬁve different areas in the visual
cortex. These ranged from the
primary visual cortex, which is the
ﬁrst cortical way station for
information arriving from the retina,
to inferotemporal cortex, thought to
be the highest stage of processing
relevant to object recognition. As
a group, these areas span the
breadth of almost every measure
one might consider relevant to this
question, predicting a broad range
of threshold sensitivities. In fact,
just the opposite was observed:
threshold current increased by only
a factor of two as increasingly
higher visual areas were
stimulated. If the threshold current
is treated as a stand-in for the
number of neurons that must be
stimulated for the animal to be
aware of the microstimulation ,
these results argue strongly that the
visual cortex is surprisingly
egalitarian in the way it accords
access to awareness.
Of course, we don’t know what
this awareness might have looked
or felt like. While Murphey and
Maunsell’s  results do not hint at
the subjective dimensions
of the effect, future experiments
might. If microstimulation
effectively reproduces normal
visual experience, as might be
expected in the early visual areas, it
should be possible to study the
visual qualities of the percept with
psychophysical approaches that
have been successfully used to
understand illusory perception.
For example, stimulation of
directionally selective neurons in
visual area MT (or V5) might
generate a perception of motion,
whose direction could be estimated
objectively by a nulling procedure
[3,19]. Especially as higher-tier
brain areas are stimulated,
however, the possibility exists that
the evoked percept is wholly unlike
anything that the animal has ever
experienced , in which case
these approaches will fail. This
would represent a fundamental
limit on what the scientiﬁc (third-
person) approach is able to tell us
about a subjective (ﬁrst-person)
experience. Maybe we will need to
teach monkeys how to talk after all.
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Howard Hughes Medical Institute and
Department of Neurobiology, 299 West
Campus Drive D200, Stanford, California
Dispersal Ecology: Where Have All
the Seeds Gone?
How effective are different animals at dispersing seeds? A new study has
traced seeds sampled in faeces to their mother of origin and concluded
that carnivorous mammals can be better dispersers than birds.
John R. Pannell
The ecological and evolutionary
success of any species ultimately
depends on its ability to disperse
and spread its genes. Most animals
do it by moving around, but
dispersal poses a serious
challenge to sessile plants. Of
course, plants have risen to the
challenge by co-opting vectors
such as wind or animals to carry
their seeds and pollen. The
mechanics of how they do it has
long fascinated biologists, but
describing the precise paths taken
has been exceedingly difﬁcult, not
least because it is the rare events
of successful long-distance
dispersal that are both the most
elusive to track down and the most
biologically far-reaching [1,2]. Most
seeds and pollen are dispersed
close to their parent plant , but
a few of them reach long distances,
and these allow the spread of
adaptations to distant populations,
Current Biology Vol 17 No 10