Direct brain recordings from neurosurgical patients listening to speech reveal that the acoustic speech signals can be reconstructed from neural activity in auditory cortex.

Rapid identification of behaviorally relevant objects is important for survival. In humans, the neural computations for visually discriminating complex objects involve inferior temporal cortex (IT). However, less detailed but faster form processing may also occur in a phylogenetically older subcortical visual system that terminates in the amygdala. We used binocular rivalry to present stimuli without conscious awareness, thereby eliminating the IT object representation and isolating subcortical visual input to the amygdala. Functional magnetic resonance imaging revealed significant brain activation in the left amygdala but not in object-selective IT in response to unperceived fearful faces compared to unperceived nonface objects. These findings indicate that, for certain behaviorally relevant stimuli, a high-level cortical representation in IT is not required for object discrimination in the amygdala.

Transcranial magnetic stimulation (TMS) is an increasingly common technique used to selectively modify neural processing. However, application of TMS is limited by uncertainty concerning its physiological effects. We applied TMS to the cat visual cortex and evaluated the neural and hemodynamic consequences. Short TMS pulse trains elicited initial activation (approximately 1 minute) and prolonged suppression (5 to 10 minutes) of neural responses. Furthermore, TMS disrupted the temporal structure of activity by altering phase relationships between neural signals. Despite the complexity of this response, neural changes were faithfully reflected in hemodynamic signals; quantitative coupling was present over a range of stimulation parameters. These results demonstrate long-lasting neural responses to TMS and support the use of hemodynamic-based neuroimaging to effectively monitor these changes over time.

The sustained negative blood oxygenation level-dependent (BOLD) response in functional MRI is observed universally, but its interpretation is controversial. The origin of the negative response is of fundamental importance because it could provide a measurement of neural deactivation. However, a substantial component of the negative response may be due to a non-neural hemodynamic artifact. To distinguish these possibilities, we have measured evoked BOLD, cerebral blood flow (CBF), and oxygen metabolism responses to a fixed visual stimulus from two different baseline conditions. One is a normal resting baseline and the other is a lower baseline induced by a sustained negative response. For both baseline conditions, CBF and oxygen metabolism responses reach the same peak amplitude. Consequently, evoked responses from the negative baseline are larger than those from the resting baseline. The larger metabolic response from negative baseline presumably reflects a greater neural response that is required to reach the same peak amplitude as that from resting baseline. Furthermore, the ratio of CBF to oxygen metabolism remains approximately the same from both baseline states (∼2:1). This tight coupling between hemodynamic and metabolic components implies that the magnitude of any hemodynamic artifact is inconsequential. We conclude that the negative response is a functionally significant index of neural deactivation in early visual cortex.