Biological constraints on stereotaxic targeting of functionally-defined cortical areas.

Understanding computational principles in hierarchically organized sensory systems requires functional parcellation of brain structures and their precise targeting for manipulations. Although brain atlases are widely used to infer area locations in the mouse neocortex, it has been unclear whether stereotaxic coordinates based on standardized brain morphology accurately represent functional domains in individual animals. Here, we used intrinsic signal imaging to evaluate the accuracy of area delineation in the atlas by mapping functionally-identified auditory cortices onto bregma-based stereotaxic coordinates.

Inhibitory gating of coincidence-dependent sensory binding in secondary auditory cortex.

Integration of multi-frequency sounds into a unified perceptual object is critical for recognizing syllables in speech. This "feature binding" relies on the precise synchrony of each component's onset timing, but little is known regarding its neural correlates. We find that multi-frequency sounds prevalent in vocalizations, specifically harmonics, preferentially activate the mouse secondary auditory cortex (A2), whose response deteriorates with shifts in component onset timings.

Recurrent network dynamics shape direction selectivity in primary auditory cortex.

Detecting the direction of frequency modulation (FM) is essential for vocal communication in both animals and humans. Direction-selective firing of neurons in the primary auditory cortex (A1) has been classically attributed to temporal offsets between feedforward excitatory and inhibitory inputs. However, it remains unclear how cortical recurrent circuitry contributes to this computation.

Reciprocal connectivity between secondary auditory cortical field and amygdala in mice.

Recent studies have examined the feedback pathway from the amygdala to the auditory cortex in conjunction with the feedforward pathway from the auditory cortex to the amygdala. However, these connections have not been fully characterized. Here, to visualize the comprehensive connectivity between the auditory cortex and amygdala, we injected cholera toxin subunit b (CTB), a bidirectional tracer, into multiple subfields in the mouse auditory cortex after identifying the location of these subfields using flavoprotein fluorescence imaging.

Associative responses to visual shape stimuli in the mouse auditory cortex.

Humans can recall various aspects of a characteristic sound as a whole when they see a visual shape stimulus that has been intimately associated with the sound. In subjects with audio-visual associative memory, auditory responses that code the associated sound may be induced in the auditory cortex in response to presentation of the associated visual shape stimulus. To test this possibility, mice were pre-exposed to a combination of an artificial sound mimicking a cat's "meow" and a visual shape stimulus of concentric circles or stars for more than two weeks, since such passive exposure is known to be sufficient for inducing audio-visual associative memory in mice.

Acute spatial spread of NO-mediated potentiation during hindpaw ischaemia in mice.

Key Points: Neuropathic pain spreads spatially beyond the injured sites, and the mechanism underlying the spread has been attributed to inflammation occurring in the spinal cord. However, the spatial spread of spinal/cortical potentiation induced by conduction block of the peripheral nerves can be observed prior to inflammation. In the present study, we found that spreading potentiation and hypersensitivity acutely induced by unilateral hindpaw ischaemia are nitric oxide (NO)-dependent and that NO is produced by ischaemia and quickly diffuses within the spinal cord.

Feedback inhibition derived from the posterior parietal cortex regulates the neural properties of the mouse visual cortex.

Feedback regulation from the higher association areas is thought to control the primary sensory cortex, contribute to the cortical processing of sensory information, and work for higher cognitive functions such as multimodal integration and attentional control. However, little is known about the underlying neural mechanisms. Here, we show that the posterior parietal cortex (PPC) persistently inhibits the activity of the primary visual cortex (V1) in mice.

Direct Relay Pathways from Lemniscal Auditory Thalamus to Secondary Auditory Field in Mice.

Tonotopy is an essential functional organization in the mammalian auditory cortex, and its source in the primary auditory cortex (A1) is the incoming frequency-related topographical projections from the ventral division of the medial geniculate body (MGv). However, circuits that relay this functional organization to higher-order regions such as the secondary auditory field (A2) have yet to be identified. Here, we discovered a new pathway that projects directly from MGv to A2 in mice.

Higher visual responses in the temporal cortex of mice.

The visual cortex of mice is a useful model for investigating the mammalian visual system. In primates, higher visual areas are classified into two parts, the dorsal stream ("where" pathway) and ventral stream ("what" pathway). The ventral stream is known to include a part of the temporal cortex.

Molecular diversity of clustered protocadherin-α required for sensory integration and short-term memory in mice.

Clustered protocadherins (Pcdhs) are neuronal cell adhesion molecules characterized by homophilic adhesion between the tetramers of 58 distinct isoforms in mice. The diversity of Pcdhs and resulting highly-specific neuronal adhesion may be required for the formation of neural circuits for executing higher brain functions. However, this hypothesis remains to be tested, because knockout of Pcdh genes produces abnormalities that may interfere with higher brain functions indirectly.

Tomographic optical imaging of cortical responses after crossing nerve transfer in mice.

To understand the neural mechanisms underlying the therapeutic effects of crossing nerve transfer for brachial plexus injuries in human patients, we investigated the cortical responses after crossing nerve transfer in mice using conventional and tomographic optical imaging. The distal cut ends of the left median and ulnar nerves were connected to the central cut ends of the right median and ulnar nerves with a sciatic nerve graft at 8 weeks of age. Eight weeks after the operation, the responses in the primary somatosensory cortex (S1) elicited by vibratory stimulation applied to the left forepaw were visualized based on activity-dependent flavoprotein fluorescence changes.

Corrigendum: Reconsidering Tonotopic Maps in the Auditory Cortex and Lemniscal Auditory Thalamus in Mice.

[This corrects the article on p. 14 in vol. 11, PMID: 28293178.

Reconsidering Tonotopic Maps in the Auditory Cortex and Lemniscal Auditory Thalamus in Mice.

The auditory thalamus and auditory cortex (AC) are pivotal structures in the central auditory system. However, the thalamocortical mechanisms of processing sounds are largely unknown. Investigation of this process benefits greatly from the use of mice because the mouse is a powerful animal model in which various experimental techniques, especially genetic tools, can be applied.

Independent tonotopy and thalamocortical projection patterns in two adjacent parts of the classical primary auditory cortex in mice.

Amid recent amendment of delineation of a mouse auditory cortical map, a caudal auditory field, originally defined as the primary auditory cortex (AI), was divided into the AI and dorsomedial field (DM), based on distinct high frequency areas. A low frequency area was not previously established in the DM because responses to low frequency tones were weak in this area. This may lead to the misconception that the DM is an atypical region that lacks a low frequency band.

Auditory cortical field coding long-lasting tonal offsets in mice.

Although temporal information processing is important in auditory perception, the mechanisms for coding tonal offsets are unknown. We investigated cortical responses elicited at the offset of tonal stimuli using flavoprotein fluorescence imaging in mice. Off-responses were clearly observed at the offset of tonal stimuli lasting for 7 s, but not after stimuli lasting for 1 s.

Quantitative map of multiple auditory cortical regions with a stereotaxic fine-scale atlas of the mouse brain.

Optical imaging studies have recently revealed the presence of multiple auditory cortical regions in the mouse brain. We have previously demonstrated, using flavoprotein fluorescence imaging, at least six regions in the mouse auditory cortex, including the anterior auditory field (AAF), primary auditory cortex (AI), the secondary auditory field (AII), dorsoanterior field (DA), dorsomedial field (DM), and dorsoposterior field (DP). While multiple regions in the visual cortex and somatosensory cortex have been annotated and consolidated in recent brain atlases, the multiple auditory cortical regions have not yet been presented from a coronal view.

Specific distribution of non-phosphorylated neurofilaments characterizing each subfield in the mouse auditory cortex.

Recent imaging studies revealed the presence of functional subfields in the mouse auditory cortex. However, little is known regarding the morphological basis underlying the functional differentiation. Distribution of particular molecules is the key information that may be applicable for identifying auditory subfields in the post-mortem brain.

Spinal mechanisms underlying potentiation of hindpaw responses observed after transient hindpaw ischemia in mice.

Transient ischemia produces postischemic tingling sensation. Ischemia also produces nerve conduction block that may modulate spinal neural circuits. In the present study, reduced mechanical thresholds for hindpaw-withdrawal reflex were found in mice after transient hindpaw ischemia, which was produced by a high pressure applied around the hindpaw for 30 min.

Delineation of a frequency-organized region isolated from the mouse primary auditory cortex.

The primary auditory cortex (AI) is the representative recipient of information from the ears in the mammalian cortex. However, the delineation of the AI is still controversial in a mouse. Recently, it was reported, using optical imaging, that two distinct areas of the AI, located ventrally and dorsally, are activated by high-frequency tones, whereas only one area is activated by low-frequency tones.

Impaired clustered protocadherin-α leads to aggregated retinogeniculate terminals and impaired visual acuity in mice.

Clustered protocadherins (cPcdhs) comprising cPcdh-α, -β, and -γ, encode a large family of cadherin-like cell-adhesion molecules specific to neurons. Impairment of cPcdh-α results in abnormal neuronal projection patterns in specific brain areas. To elucidate the role of cPcdh-α in retinogeniculate projections, we investigated the morphological patterns of retinogeniculate terminals in the lateral geniculate (LG) nucleus of mice with impaired cPcdh-α.

The extrageniculate visual pathway generates distinct response properties in the higher visual areas of mice.

Background: Visual information conveyed through the extrageniculate visual pathway, which runs from the retina via the superior colliculus (SC) and the lateral posterior nucleus (LPN) of the thalamus to the higher visual cortex, plays a critical role in the visual capabilities of many mammalian species. However, its functional role in the higher visual cortex remains unclear. Here, we observed visual cortical area activity in anesthetized mice to evaluate the role of the extrageniculate pathway on their specialized visual properties.

Visual map shifts based on whisker-guided cues in the young mouse visual cortex.

Mice navigate nearby space using their vision and whiskers, and young mice learn to integrate these heterogeneous inputs in perceptual space. We found that cortical responses were depressed in the primary visual cortex of young mice after wearing a monocular prism. This depression was uniformly observed in the primary visual cortex and was eliminated by whisker trimming or lesions in the posterior parietal cortex.