Anatomical Evidence of Multimodal Integration in Primate Striate Cortex

“Histological studies demonstrate that exuberant projections from the auditory to the visual cortex existing in newborn kittens and macaque monkeys are gradually eliminated during the synaptic pruning phase [33–36], with only a small fraction of these projections being maintained into adulthood [37, 38].”

“Connections between auditory cortex and parts of areas 17 and 18 were noted in anatomical studies of macaque monkeys (Falchier et al 2002; Rockland and Ojima 2003).”

“Anatomical connections between sensory modalities exist at early stages of the cortical processing hierarchy, such as between auditory and visual cortex (Falchier et al., 2002; Rockland and Ojima, 2003; Bizley et al., 2007) and between somatosensory and auditory cortex (Schroeder et al., 2001).”

“This is not a simple issue, as even well-defined areas show some regional variation in their pattern of cortical inputs (Falchier et al. 2002; Palmer and Rosa 2006a).”

“Previous studies have demonstrated the existence of a direct projection from A1 to primary visual cortex (V1) in primates (Falchier et al., 2002; Rockland and Ojima, 2003).”

“It is likely that the same anatomical projections from multisensory areas to V1 are present in normal individuals [Falchier et al., 2002]; however, this influence on the earliest visual processing centers has not previously been shown in healthy adults for language related stimuli.”

“…areas—is consistent with the existence of direct connections between the auditory cortex and the primary visual cortex (Rockland & Ojima, 2003; Falchier, Clavagnier, Barone, & Kennedy, 2002), and multisensory neurons in low-level sensory areas, such as auditory-sensitive neurons in the visual…”

“The normal brain utilizes heavy crosstalk between the senses, as evidenced by anatomical tracing [32] [33] [34] [35], sensory substitution experiments [36], and cross-sensory illusions [37] [38] [39] [40].”

“Bidirectional connections involving caudal auditory areas have been demonstrated, both going to peripheral V1 and V2 [36,37] and originating from peripheral V2 [20], which could potentially subserve the crossmodal recruitment observed in both deaf and blind individuals, respectively.”

“Some reports have revealed the xistence of such connections between the visual and auditory corices [25,85] and between tactile and auditory cortices [33] which ould embody early interactions.”

“Recent studies have shown that there are direct projections from primary auditory cortex (A1) to primary visual cortex (V1) in the mature primate brain although they are primarily found in regions representing peripheral vision (Rockland & Ojima, 2003; Falchier, Clavagnier, Barone, & Kennedy, 2002).”

“Other studies have also shown direct anatomical connections between auditory and visual cortex at early stages of the cortical processing hierarchy (Falchier et al. 2002; Rockland and Ojima 2003; Clavagnier et al. 2004; Bizley et al. 2007).”

“This indicates that the STS may be modulating the effects within low-level visual areas possibly by feedback connections (e.g. Falchier et al., 2002; Noesselt et al., 2007).”

“However, anatomical evidence confirms the existence of direct connections between primary sensory areas within the nonhuman primate brain (Falchier et al., 2002; Rockland and Ojima, 2003; Cappe and Barone, 2005), suggesting that this view may be an oversimplification.”

“In addition, projections from non-visual extrastriate cortical areas to V1 seem to target the peripheral visual cortex but not the central visual cortex [8].”

“The loss of auditory input in direct projections from auditory to visual areas (Falchier et al., 2002) could possibly enhance susceptibility of visual areas to visual inputs and visual top–down control (Bavelier et al., 2006).”

“…to the visual system, in which a growing body of evidence supports the idea that auditory cortical regions project to both primary visual cortex (Falchier et al., 2002; Rockland and Ojima, 2003; Clavagnier et al., 2004; Hall and Lomber, 2008) and extrastriate visual cortical regions (Clemo et…”

“The observation that caudal auditory cortex is connected with early peripheral visual representations suggests a ‘‘dorsal-stream” type function of these multisensory connections (Falchier et al., 2002).”

“…our results suggest that previous reports showing projections from VI to SI (Miller and Vogt, 1984; Olavarria and Montero, 1984) and to AI in cats (Falchier et al., 2002; Hall and Lomber, 2008) and in rats (Miller and Vogt, 1984) and from SI to AI (Budinger et al., 2006) possibly also included a…”

“First, these effects may reflect cross-sensory driving and/or inhibition of lowerorder sensory areas via direct projections from one sensory cortex to another (Falchier et al. 2002; Rockland and Ojima 2003; review in Schroeder et al. 2004).”

“By probing sensory systems with multisensory input, these studies have provided ample evidence that sensory processing is influenced, even at the level of primary sensory cortex, by heteromodal stimuli (vision [8, 30–32]; audition [9, 10, 33]; gustation [15, 34]; and olfaction [11, 35, 36]).”

“…optimizes perception and behavior, as shown in error detection and reaction time measurements, particularly in “low sensory input” situations, where limited sensory information makes perceptual judgments difficult (Bolognini et al., 2005; Frassinetti et al., 2002; McDonald et al., 2000).”

“Another possibility is the discovery of a direct connection between SI and V1, similar to that of the primary auditory and visual cortices (Falchier et al., 2002).”

“In conjunction with other anatomical studies that have also shown projections from the auditory cortex into the primary visual cortex (Falchier et al. 2002; Rockland and Ojima 2003), these results suggest that even”

“activation in the early visual cortex [ 3 , 4, 14, 21].”

“Unlike Cecere et al. (2015) 32 , we presented both one and two flash stimuli in the periphery, because auditory influences on visual cortices are more pronounced in the periphery 53,54 .”

“Do blind individuals systematically outperform their sighted counterparts in sensory and cognitive processes?”

“While the historical tracing studies mostly contain qualitative information, more recent studies have aimed at building a quantitative connectivity database of the macaque brain (Falchier et al., 2002; Markov et al., 2014; Markov et al., 2011) (core-nets.”

“For example, in non-human primates, anatomical connections between primary auditory cortex and primary visual cortex have been demonstrated [35] and in humans, a recent neuroimaging study using effective connectivity analysis demonstrated that activity in auditory cortex is modulated by both direct connections between…”

“In the macaque monkey, even between primary visual and auditory cortices, interconnectivity has been shown using anterograde tracer injections (Rockland and Ojima, 2003; Falchier et al., 2002).”

“Unlike the auditory system that is neocortical and has direct and close connections with the targeted visual cortex (Falchier et al., 2002; Kayser et al., 2008; Novak et al., 2015), the olfactory system is largely subcortical or paleocortical without direct connections with visual cortex (Carmichael et al.”

“We suggest the retina as an additional site for plasticity in the deaf because it is far from fully developed at birth, requiring an unimpeded optical system to achieve normal development [18,19] and because peripheral vision in hearing individuals appears to receive input from auditory stimuli at cortical level, sugg…”

“Although the direct pathway has not been clarified in infants, neurophysiological and neuroimaging studies on animals and human adults provide multiple evidence (Bavelier and Neville, 2002; Falchier et al., 2002; Rockland and Ojima, 2003; Eckert et al., 2008).”

“The inverse pathway corresponded to a descending pathway and further showed homology to a well-known descending pathway, namely, the corticothalamic pathway that originates in layer 6.”

“…of primary sensory areas via back-projections from higher-order areas or from direct projections from the piriform cortex to visual cortex and vice versa, as has been recently indicated in the case of vision and audition and vision and touch (Falchier et al. 2002; Rockland and Ojima 2002).”

“Based on this model, audiovisual integration may partly occur via direct communication between visual and auditory cortices in which traditional unisensory regions may have multisensory characteristics (Calvert et al. 1997; Foxe et al. 2000; Shams et al. 2001; Falchier et al. 2002; Rockland and Ojima 2003; Brosch et a…”

“…cortex have been shown in the cat (Innocenti et al., 1988; Sanchez-Vives et al., 2006; Hall & Lomber, 2008), hamster (Izraeli et al., 2002), monkey (Falchier et al., 2002; Rockland & Ojima, 2003; Clavagnier et al., 2004; Cappe & Barone, 2005), ferret (Allman et al., 2008), Mongolian gerbil…”

“This suggests that direct connections between auditory and visual areas may be responsible for the generationofthiscomponent(Mishraetal.,2007).Suchconnections have been characterized in recent years in anatomical labeling studies in primates (Clavagnier, Falchier, & Kennedy,2004;RocklandO Falchier,Clavagnier, Barone,…”

“The most likely anatomical substrates for this cross-modal interaction are corticocortical connections among higher association and sensory areas (Falchier et al., 2002; Rockland & Ojima, 2003; Cappe & Barone, 2005; Budinger et al., 2006).”

“Bidirectional connections between primary sensory cortices are known to exist in primates (Falchier et al., 2002) and other animals.”

“, in press)—including recent evidence, in monkeys, of anatomical projections from auditory cortex to visual cortex (Falchier et al., 2002; Rockland and Ojima, 2003) and feedforward (ascending) visual input to posterior auditory association cortex (Schroeder and Foxe, 2002).”

“However, feedback connections from convergence zones, such as pSTS, still seem to clearly outnumber direct connections between early sensory-specific cortices (Falchier et al. 2002).”

“Furthermore, Falchier et al. (2002) speciWcally tested for the possibility of reciprocal connections by placing retrograde tracers into auditory cortex of the monkey and failed to label any neurons in area 17.”

“Similarly, both anatomical [17,62,63,64] and electrophysiological animal studies [65,66] have shown that the early stages of sensory processing, including V1 [67], are involved in multisensory processing [68].”

“For example, direct cortical projections between primary auditory and visual cortices have now been documented in the primate brain (Cappe et al. 2009; Clavagnier et al. 2004; Falchier et al. 2002, 2010; Musacchia and Schroeder 2009; Rockland and Ojima 2003; Smiley and Falchier 2009).”

“In addition to visual inputs, V1 and V2 receive feedback (FB) from auditory and parietal cortices suggesting that multimodal signals are available to all visual areas, not just to association areas positioned at higher levels of the anatomical hierarchy (Falchier et al. 2002; Rockland and Ojima 2003).”

“Current trends suggest that similar reinterpretations may even apply to primary sensory cortices, which are known to receive feedback projections from other sensory modalities (Falchier et al. 2002; Rockland and Ijima 2003).”

“In non-human primates, the existence of projections from primary and secondary auditory fields to striate and extra-striate cortex have been described (Falchier et al., 2002; Schroeder & Foxe, 2005).”

“…projections from “non-specific” thalamic inputs (Hackett et al., 1998b; Jones, 1998), feedback projections from higher-order multi-sensory cortical regions (Hackett et al., 1998a), and direct lateral projections from low-level nonauditory cortices (Cappe and Barone, 2005; Falchier et al., 2002).”

“For example, anatomical tracing studies in monkeys have demonstrated connections from the core and belt auditory regions to primary visual areas (Falchier et al., 2002; Rockland and Ojima, 2003).”

“Multisensory convergence in primary visual cortex has been found in the macaque brain [27], and recently the primary visual cortex of rodents has been shown to respond to haptic exploration of novel objects [28], its response correlating with the animal’s performance in a tactile aperture discrimination task.”

“Likewise, central vs peripheral portions of macaque area V1 have different patterns and strengths of connectivity with extrastriate visual areas (Falchier et al., 2002).”

“This supports a functional role for connections between auditory cortex and peripheral visual representations, as is also indicated by anatomical connectivity studies (Falchier et al., 2002; Rockland and Ojima, 2003).”

“…several anatomical studies in monkeys (auditory cortex: Falchier et al., 2002; Rockland and Ojima, 2003; area STP in the superior temporal sulcus: Falchier et al., 2002; perirhinal cortex: Clavagnier et al., 2004; and areas TF and TH in the parahippocampal gyrus: Doty, 1983; Kennedy and Bullier,…”

“In [29], the authors showed the greater capacity of deep architectures to extract meaningful dimensions from large datasets, compared with classical dimensionality reduction techniques such as PCA.”

“This hypothesis has received indirect support from the recent anatomical finding of direct projections from both the auditory cortex and the polysensory superior temporal cortex to the primary visual cortex in the monkey ( Falchier, Clavagnier, Barone, & Kennedy, 2002 ).”

“Such connections have been evidenced in the monkey (Falchier et al., 2002; Rockland and Ojima, 2003).”

“An alternative hypothesis is that the visual areas receive non-visual sensory information through corticocortical connections between these sensory modalities [45,84], which is supported by task-based fMRI studies [85,86], and a resting-state fMRI study [87] in sighted subjects, an effective connectivity study [63], a…”

“We did not observe any integrative effects from bimodal visuo-tactile stimuli in lower levels, traditionally unisensory cortices, despite prior evidence of anatomical connections in primates (Falchier et al., 2002; Rockland and Ojima, 2003; Cappe and Barone, 2005) as well as apparent multimodal interactions in human n…”

“ORIGINAL RESEARCH ARTICLE published: 22 April 2014 doi: 10.3389/fnins.2014.00072 Feedforward and feedback projections of caudal belt and parabelt areas of auditory cortex: refining the hierarchical model”

“Generally an eccentricity of 5–20u has been used in studies of the illusion, with most studies presenting stimuli within the range where connections from primary auditory to primary visual cortex have been found subserving the visual periphery [25].”

“Finally, connections with auditory temporal regions have been reported for dorsal prefrontal cortex (Romanski et al. 1999) and primary visual cortex (Falchier et al. 2002).”

“2007) that have previously been shown to receive direct anatomical projections from the core and parabelt areas of the auditory cortex (Falchier et al. 2002).”

“There is evidence in support of direct, but sparse, anatomical links between the auditory and striate cortices of the nonhuman primate brain [22, 69, 93].”

“Anatomical evidence for direct connections between primary auditory cortex and primary visual cortex in adult monkeys has been previously reported [133].”

“, 2014) cortex, and the predominant trend in primate cortex (Falchier et al., 2002).”