Transcranial magnetic stimulation has been used to investigate almost all areas of cognitive neuroscience. This article discusses the most important (and least understood) considerations regarding the use of transcranial magnetic stimulation for cognitive neuroscience and outlines advances in the use of this technique for the replication and extension of findings from neuropsychology. We also take a more speculative look forward to the emerging development of strategies for combining transcranial magnetic stimulation with other brain imaging technologies and methods in the cognitive neurosciences.

The lack of an accepted measure of awareness has made claims that accurate decisions can be made without awareness controversial. Here we introduce a new objective measure of awareness, post-decision wagering. We show that participants fail to maximize cash earnings by wagering high following correct decisions in blindsight, the Iowa gambling task and an artificial grammar task. This demonstrates, without the uncertainties associated with the conventional subjective measures of awareness (verbal reports and confidence ratings), that the participants were not aware that their decisions were correct. Post-decision wagering may be used to study the neural correlates of consciousness.

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The number of GABA-immunoreactive [GABA(+)] neurons and synapses was determined in functionally distinct subregions delineated as rich and poor in cytochrome oxidase (CO) in the visual cortex of adult macaque monkeys. The average numerical density (number per unit volume, Nv) of GABA(+) neurons and synapses was not significantly different between the CO-rich and -poor regions. Twenty percent of the total number of cortical neurons and 17% of the synapses were GABA(+). On average, each visual cortical neuron receives 3900 synapses, 660 of them being GABA(+). The latter were distributed on the target cell in a pattern that predicts the site of GABA influences in cortex. The major targets of GABA(+) synapses were dendritic shafts, comprising nearly two-thirds of the postsynaptic elements. About every fourth and every eighth GABA(+) synapse was devoted to dendritic spines and to neuronal somata, respectively. Axon initial segments, although the exclusive targets of GABA(+) cells, comprise less than 0.1% of structures postsynaptic to GABA(+) boutons. From this distribution, we estimate that in each cubic millimeter of striate cortex there were about 20 million GABA(+) synapses on dendritic spines, 47 million on dendritic trunks, 9 million on somata, and fewer than 0.1 million on axon initial segments. The sites of influences of GABA-immunonegative [GABA(-)] synapses were different in that they target mainly dendritic spines and dendritic trunks. About two-thirds of GABA(-) synapses were on dendritic spines, and the remainder were devoted to dendritic trunks. Only a minute fraction innervate somata. We estimate that in 1 mm3 of striate cortex there were about 235 million GABA(-) synapses on spines, 133 million on dendrites, and about 2 million on somata. The proportions of GABA(+) neurons and synapses and their target distribution did not appreciably differ from those of the visual cortex of the cat even though the numerical density of neurons was 2.5 times higher in the monkey.

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